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 02[[:space:]]-[[:space:]]Core[[:space:]]Java/005[[:space:]]First[[:space:]]code[[:space:]]Setup.mp4 filter=lfs diff=lfs merge=lfs -text
 02[[:space:]]-[[:space:]]Core[[:space:]]Java/009[[:space:]]Literal.mp4 filter=lfs diff=lfs merge=lfs -text
 02[[:space:]]-[[:space:]]Core[[:space:]]Java/008[[:space:]]Data[[:space:]]Types.mp4 filter=lfs diff=lfs merge=lfs -text
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+02[[:space:]]-[[:space:]]Core[[:space:]]Java/012[[:space:]]Arithmetic[[:space:]]Operators.mp4 filter=lfs diff=lfs merge=lfs -text
+02[[:space:]]-[[:space:]]Core[[:space:]]Java/010[[:space:]]Type[[:space:]]Conversion.mp4 filter=lfs diff=lfs merge=lfs -text
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+02[[:space:]]-[[:space:]]Core[[:space:]]Java/017[[:space:]]Ternary.mp4 filter=lfs diff=lfs merge=lfs -text
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+02[[:space:]]-[[:space:]]Core[[:space:]]Java/019[[:space:]]Need[[:space:]]For[[:space:]]Loop.mp4 filter=lfs diff=lfs merge=lfs -text

02 - Core Java/006 How Java Works.mp4

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02 - Core Java/039 Mutable vs Immutable string_en.srt

@@ -0,0 +1,688 @@
+1
+00:00:00,000 --> 00:00:03,000
+(gentle piano music)
+
+2
+00:00:03,000 --> 00:00:04,000
+-: So in the previous video we have talked
+
+3
+00:00:04,000 --> 00:00:05,000
+about string, right?
+
+4
+00:00:05,000 --> 00:00:08,000
+Now we talk about this string,
+
+5
+00:00:08,000 --> 00:00:10,000
+what might be happening behind the scene.
+
+6
+00:00:10,000 --> 00:00:11,000
+Example, let's say if you store this navin,
+
+7
+00:00:11,000 --> 00:00:15,000
+of course it'll be getting stored in the heap memory.
+
+8
+00:00:15,000 --> 00:00:16,000
+But now what I wanna do is
+
+9
+00:00:16,000 --> 00:00:17,000
+before printing navin here,
+
+10
+00:00:17,000 --> 00:00:19,000
+let's say I want to append something.
+
+11
+00:00:19,000 --> 00:00:22,000
+So I would say name is equal to,
+
+12
+00:00:22,000 --> 00:00:25,000
+I want to add my name with, let's say reddy here.
+
+13
+00:00:25,000 --> 00:00:26,000
+I'm giving a space
+
+14
+00:00:26,000 --> 00:00:28,000
+so that we can differentiate these two words.
+
+15
+00:00:28,000 --> 00:00:30,000
+So of course now when I say name,
+
+16
+00:00:30,000 --> 00:00:32,000
+it'll be Navin Reddy, right?
+
+17
+00:00:32,000 --> 00:00:34,000
+So basically we are trying to change the value.
+
+18
+00:00:34,000 --> 00:00:36,000
+Now if we talk about integer, float, double.
+
+19
+00:00:36,000 --> 00:00:38,000
+Basically you can change values of it, right?
+
+20
+00:00:38,000 --> 00:00:39,000
+And it actually makes sense.
+
+21
+00:00:39,000 --> 00:00:42,000
+That's why we call them as variables.
+
+22
+00:00:42,000 --> 00:00:43,000
+And here also, we are trying to do that.
+
+23
+00:00:43,000 --> 00:00:46,000
+But first of all, let's check if this works.
+
+24
+00:00:46,000 --> 00:00:50,000
+So if I go back and compile and run, it works.
+
+25
+00:00:50,000 --> 00:00:51,000
+You can see that the new data
+
+26
+00:00:51,000 --> 00:00:52,000
+for the navin is navin reddy, right?
+
+27
+00:00:52,000 --> 00:00:54,000
+And that works.
+
+28
+00:00:54,000 --> 00:00:56,000
+But what if I say that's not the case?
+
+29
+00:00:56,000 --> 00:00:59,000
+You're not changing the existing string.
+
+30
+00:00:59,000 --> 00:01:00,000
+Let me repeat.
+
+31
+00:01:00,000 --> 00:01:04,000
+You are not changing from navin to navin reddy?
+
+32
+00:01:04,000 --> 00:01:07,000
+So if you're thinking there will be a variable here
+
+33
+00:01:07,000 --> 00:01:10,000
+where you have Navin, you're making it Navin Reddy.
+
+34
+00:01:10,000 --> 00:01:12,000
+No, that's not the case.
+
+35
+00:01:12,000 --> 00:01:14,000
+That's not how string works.
+
+36
+00:01:14,000 --> 00:01:15,000
+Okay, so what happens?
+
+37
+00:01:15,000 --> 00:01:18,000
+So what I will do is I'll just remove this part now.
+
+38
+00:01:18,000 --> 00:01:20,000
+So what is happening, basically,
+
+39
+00:01:20,000 --> 00:01:23,000
+you know, since strings are used heavily in Java,
+
+40
+00:01:23,000 --> 00:01:26,000
+now most of the time you try to reuse the strings,
+
+41
+00:01:26,000 --> 00:01:28,000
+the same string, you'll be using multiple times.
+
+42
+00:01:28,000 --> 00:01:31,000
+Example, let's say, before I show you something,
+
+43
+00:01:31,000 --> 00:01:33,000
+let's say, I create a string here,
+
+44
+00:01:33,000 --> 00:01:37,000
+which is s1 is equal to Navin.
+
+45
+00:01:37,000 --> 00:01:38,000
+And you can see we have a capital N this time.
+
+46
+00:01:38,000 --> 00:01:41,000
+So this two data are actually different, okay?
+
+47
+00:01:41,000 --> 00:01:44,000
+So I will say string s2 is equal to,
+
+48
+00:01:44,000 --> 00:01:45,000
+and I will say Navin again.
+
+49
+00:01:45,000 --> 00:01:47,000
+Now, what do you think?
+
+50
+00:01:47,000 --> 00:01:50,000
+How many objects we are creating behind the scene?
+
+51
+00:01:50,000 --> 00:01:51,000
+Think about this.
+
+52
+00:01:51,000 --> 00:01:51,000
+Okay?
+
+53
+00:01:51,000 --> 00:01:53,000
+So if you're thinking, we got two objects,
+
+54
+00:01:53,000 --> 00:01:57,000
+actually not, we got two references.
+
+55
+00:01:57,000 --> 00:01:58,000
+We got s1, s2.
+
+56
+00:01:58,000 --> 00:02:02,000
+Of course, in your stack, you'll be having s1, s2 here,
+
+57
+00:02:02,000 --> 00:02:06,000
+but in total, you got only one object.
+
+58
+00:02:08,000 --> 00:02:09,000
+And that sounds tricky here, right?
+
+59
+00:02:09,000 --> 00:02:11,000
+And let me prove that point to you.
+
+60
+00:02:11,000 --> 00:02:13,000
+See, what I want to prove is the value
+
+61
+00:02:13,000 --> 00:02:15,000
+for this field and this field will be equal.
+
+62
+00:02:15,000 --> 00:02:17,000
+The way the I can do that is by saying S out,
+
+63
+00:02:17,000 --> 00:02:22,000
+s1 is equal to equal to s2.
+
+64
+00:02:22,000 --> 00:02:25,000
+If this is true, then they are same.
+
+65
+00:02:25,000 --> 00:02:27,000
+So if I run, you can see we got true.
+
+66
+00:02:27,000 --> 00:02:31,000
+That means the value for the addresses are same.
+
+67
+00:02:31,000 --> 00:02:33,000
+In total we got only one object.
+
+68
+00:02:33,000 --> 00:02:37,000
+So here what happens is we have a special area
+
+69
+00:02:37,000 --> 00:02:39,000
+inside your heap memory.
+
+70
+00:02:39,000 --> 00:02:42,000
+So this is your heap, that's your JVM,
+
+71
+00:02:42,000 --> 00:02:44,000
+and that's your stack.
+
+72
+00:02:44,000 --> 00:02:45,000
+So inside your heap,
+
+73
+00:02:45,000 --> 00:02:50,000
+you'll be having a special area called string constant pool.
+
+74
+00:02:51,000 --> 00:02:54,000
+And by the name itself you can see it says constant.
+
+75
+00:02:54,000 --> 00:02:55,000
+That's right.
+
+76
+00:02:55,000 --> 00:02:58,000
+Every string which you create, which you use in Java,
+
+77
+00:02:58,000 --> 00:03:01,000
+which is a string literal is actually a constant.
+
+78
+00:03:01,000 --> 00:03:01,000
+You can't change it.
+
+79
+00:03:01,000 --> 00:03:04,000
+Example, if I write something like navin here,
+
+80
+00:03:04,000 --> 00:03:05,000
+I cannot change it.
+
+81
+00:03:05,000 --> 00:03:06,000
+It's done.
+
+82
+00:03:06,000 --> 00:03:08,000
+It's navin everywhere, okay?
+
+83
+00:03:08,000 --> 00:03:10,000
+So you can't change the data.
+
+84
+00:03:10,000 --> 00:03:12,000
+So example, what happens is every time you try
+
+85
+00:03:12,000 --> 00:03:14,000
+to use a variable here, example,
+
+86
+00:03:14,000 --> 00:03:16,000
+if you execute the line number eight, it checks,
+
+87
+00:03:16,000 --> 00:03:18,000
+okay, we need navin variable.
+
+88
+00:03:18,000 --> 00:03:21,000
+Do we already have navin in the string constant pool?
+
+89
+00:03:21,000 --> 00:03:22,000
+No, we don't have it.
+
+90
+00:03:22,000 --> 00:03:23,000
+So let's create navin here.
+
+91
+00:03:23,000 --> 00:03:25,000
+So it'll create a string variable, navin,
+
+92
+00:03:25,000 --> 00:03:27,000
+it'll have some address, let's say 101,
+
+93
+00:03:27,000 --> 00:03:31,000
+and then the name variable here will get this address.
+
+94
+00:03:31,000 --> 00:03:33,000
+So this name variable is actually referring
+
+95
+00:03:33,000 --> 00:03:36,000
+to this particular address, okay?
+
+96
+00:03:36,000 --> 00:03:38,000
+Then it goes for the next statement.
+
+97
+00:03:38,000 --> 00:03:39,000
+Let's execute this part.
+
+98
+00:03:39,000 --> 00:03:41,000
+Let's ignore this line as of now,
+
+99
+00:03:41,000 --> 00:03:42,000
+let's focus on line number 12 and 13.
+
+100
+00:03:42,000 --> 00:03:45,000
+So line number 12 says, s1 is equal to Navin.
+
+101
+00:03:45,000 --> 00:03:46,000
+Okay, so it checks,
+
+102
+00:03:46,000 --> 00:03:49,000
+do we have navin with capital N in the string pool?
+
+103
+00:03:49,000 --> 00:03:50,000
+No, we don't have it.
+
+104
+00:03:50,000 --> 00:03:52,000
+So it'll create Navin here.
+
+105
+00:03:52,000 --> 00:03:54,000
+And let's say the address is 103.
+
+106
+00:03:54,000 --> 00:03:57,000
+So it'll store 103 here.
+
+107
+00:03:57,000 --> 00:03:58,000
+Now that makes sense, right?
+
+108
+00:03:58,000 --> 00:04:00,000
+And that's why you're referring to that particular location.
+
+109
+00:04:00,000 --> 00:04:02,000
+Now, what happens on line number 13?
+
+110
+00:04:02,000 --> 00:04:05,000
+Line number 13 says string s2 is equal to Navin.
+
+111
+00:04:05,000 --> 00:04:07,000
+It'll go to string constant pool again
+
+112
+00:04:07,000 --> 00:04:09,000
+and check, hey, do we have Navin with capital N?
+
+113
+00:04:09,000 --> 00:04:10,000
+Yes, we do have.
+
+114
+00:04:10,000 --> 00:04:13,000
+Now, it'll not create a new object for you,
+
+115
+00:04:13,000 --> 00:04:16,000
+it'll simply use this address 103.
+
+116
+00:04:16,000 --> 00:04:17,000
+Okay?
+
+117
+00:04:17,000 --> 00:04:18,000
+And that's the beauty.
+
+118
+00:04:18,000 --> 00:04:20,000
+That's how you're trying to save the memory.
+
+119
+00:04:20,000 --> 00:04:23,000
+Otherwise you could have created multiple variables
+
+120
+00:04:23,000 --> 00:04:24,000
+with the same data.
+
+121
+00:04:24,000 --> 00:04:25,000
+So it doesn't make sense, right?
+
+122
+00:04:25,000 --> 00:04:27,000
+And that's why it uses a string constant pool.
+
+123
+00:04:27,000 --> 00:04:30,000
+Now, my question to you is, what is happening here?
+
+124
+00:04:30,000 --> 00:04:33,000
+Now when I say you can't change the data,
+
+125
+00:04:33,000 --> 00:04:36,000
+that means you cannot simply update this particular
+
+126
+00:04:36,000 --> 00:04:37,000
+navin by Navin Reddy?
+
+127
+00:04:37,000 --> 00:04:40,000
+No, that's not happening, navin is still there.
+
+128
+00:04:40,000 --> 00:04:42,000
+It's a constant. You can't change this.
+
+129
+00:04:42,000 --> 00:04:43,000
+Now on line number 9,
+
+130
+00:04:43,000 --> 00:04:47,000
+what is happening is it is creating a new object
+
+131
+00:04:47,000 --> 00:04:51,000
+which will have a data which is navin reddy,
+
+132
+00:04:51,000 --> 00:04:53,000
+let's say it has the address, which is 105.
+
+133
+00:04:53,000 --> 00:04:54,000
+So on line number 9,
+
+134
+00:04:54,000 --> 00:04:58,000
+basically what you're doing is you are changing this address
+
+135
+00:04:58,000 --> 00:05:01,000
+from 101 to 105.
+
+136
+00:05:01,000 --> 00:05:04,000
+You are just changing the address.
+
+137
+00:05:04,000 --> 00:05:06,000
+You're not changing the actual data.
+
+138
+00:05:06,000 --> 00:05:09,000
+You are basically creating a new object.
+
+139
+00:05:09,000 --> 00:05:09,000
+Okay?
+
+140
+00:05:09,000 --> 00:05:12,000
+Now, you might be thinking what will happen to navin here?
+
+141
+00:05:12,000 --> 00:05:13,000
+The thing is,
+
+142
+00:05:13,000 --> 00:05:16,000
+now this particular object is eligible
+
+143
+00:05:16,000 --> 00:05:17,000
+for garbage collection.
+
+144
+00:05:17,000 --> 00:05:19,000
+It'll be removed after some time,
+
+145
+00:05:19,000 --> 00:05:21,000
+just to get some memory back.
+
+146
+00:05:21,000 --> 00:05:22,000
+Okay?
+
+147
+00:05:22,000 --> 00:05:24,000
+So point to remember is once you create this object,
+
+148
+00:05:24,000 --> 00:05:25,000
+you can't change it.
+
+149
+00:05:25,000 --> 00:05:28,000
+And that's where we have some terms to remember.
+
+150
+00:05:28,000 --> 00:05:29,000
+And the terms are,
+
+151
+00:05:29,000 --> 00:05:33,000
+so there's a concept of mutable strings
+
+152
+00:05:33,000 --> 00:05:35,000
+and immutable string.
+
+153
+00:05:35,000 --> 00:05:36,000
+Now, what is mutable means?
+
+154
+00:05:36,000 --> 00:05:40,000
+Mutable means change something which can be changed.
+
+155
+00:05:40,000 --> 00:05:43,000
+And immutable means unchanged or you cannot change it.
+
+156
+00:05:43,000 --> 00:05:46,000
+So basically, by default strings are immutable.
+
+157
+00:05:46,000 --> 00:05:48,000
+Once you create the object, you can't change it.
+
+158
+00:05:48,000 --> 00:05:49,000
+And that's very important remember,
+
+159
+00:05:49,000 --> 00:05:51,000
+it's immutable string, okay?
+
+160
+00:05:51,000 --> 00:05:53,000
+So whatever data you're creating here is immutable.
+
+161
+00:05:53,000 --> 00:05:55,000
+But what if you want mutable string?
+
+162
+00:05:55,000 --> 00:05:58,000
+And that's why we have two different classes in Java to use.
+
+163
+00:05:58,000 --> 00:06:00,000
+Instead of using string,
+
+164
+00:06:00,000 --> 00:06:04,000
+you can use something called a string buffer
+
+165
+00:06:04,000 --> 00:06:07,000
+or a string builder.
+
+166
+00:06:07,000 --> 00:06:09,000
+Now, both are very similar with one difference
+
+167
+00:06:09,000 --> 00:06:10,000
+that defense we'll discuss later,
+
+168
+00:06:10,000 --> 00:06:14,000
+but they both are similar and they both provide you a way
+
+169
+00:06:14,000 --> 00:06:18,000
+to implement a immutable string.
+
+170
+00:06:18,000 --> 00:06:18,000
+Okay?
+
+171
+00:06:18,000 --> 00:06:19,000
+Now, how do we do that?
+
+172
+00:06:19,000 --> 00:06:22,000
+That we'll see in the upcoming videos.
+

02 - Core Java/039 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/040 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/040 StringBuffer and StringBuilder_en.srt

@@ -0,0 +1,620 @@
+1
+00:00:00,000 --> 00:00:03,000
+(soft chimes)
+
+2
+00:00:03,000 --> 00:00:05,000
+-: In this video, we'll work with string buffer.
+
+3
+00:00:05,000 --> 00:00:07,000
+So, what we have is we have a string anvil
+
+4
+00:00:07,000 --> 00:00:09,000
+and we have work with it, right?
+
+5
+00:00:09,000 --> 00:00:11,000
+So I'll do is remove everything
+
+6
+00:00:11,000 --> 00:00:13,000
+and let's work with string buffer.
+
+7
+00:00:13,000 --> 00:00:15,000
+So I'll say string buffer
+
+8
+00:00:15,000 --> 00:00:16,000
+and lets create a reference call it
+
+9
+00:00:16,000 --> 00:00:19,000
+equal to new... string buffer
+
+10
+00:00:19,000 --> 00:00:21,000
+so when we talk about string buffer
+
+11
+00:00:21,000 --> 00:00:22,000
+of course in this string buffer, you will have a string
+
+12
+00:00:22,000 --> 00:00:25,000
+and if which is actually mutable
+
+13
+00:00:25,000 --> 00:00:26,000
+you can change it...
+
+14
+00:00:26,000 --> 00:00:27,000
+now to make it more efficient
+
+15
+00:00:27,000 --> 00:00:28,000
+you know what string buffer does?
+
+16
+00:00:28,000 --> 00:00:31,000
+String buffer will give you a "buffer size".. okay?
+
+17
+00:00:31,000 --> 00:00:33,000
+Which is of 16 bytes
+
+18
+00:00:33,000 --> 00:00:34,000
+so I can. I can just try to print that first
+
+19
+00:00:34,000 --> 00:00:36,000
+I will say sb. 'dot'
+
+20
+00:00:36,000 --> 00:00:39,000
+so we can know the capacity of the string buffer
+
+21
+00:00:39,000 --> 00:00:41,000
+even if its empty, it will give a capacity
+
+22
+00:00:41,000 --> 00:00:43,000
+of 16 characters and you got it there .
+
+23
+00:00:43,000 --> 00:00:46,000
+In fact, you can also provide some initial string here,..
+
+24
+00:00:46,000 --> 00:00:48,000
+So let's say.. uhh... if I say
+
+25
+00:00:48,000 --> 00:00:48,000
+"Navin" here
+
+26
+00:00:48,000 --> 00:00:51,000
+now Navin is a 5 charters right? This is how
+
+27
+00:00:51,000 --> 00:00:53,000
+you basically create a string buffer.. in bracket
+
+28
+00:00:53,000 --> 00:00:54,000
+you will mention the string
+
+29
+00:00:54,000 --> 00:00:56,000
+so, it will create a string buffer object
+
+30
+00:00:56,000 --> 00:00:59,000
+and the beauty is you can change this data.
+
+31
+00:00:59,000 --> 00:01:02,000
+Okay.. now the thing is..uhh.. if you talk about
+
+32
+00:01:02,000 --> 00:01:03,000
+capacity what it will be?..
+
+33
+00:01:03,000 --> 00:01:06,000
+So capacity is..it should be still 16 right?
+
+34
+00:01:06,000 --> 00:01:07,000
+No. It actually changes
+
+35
+00:01:07,000 --> 00:01:10,000
+if you can see.. the capacity will become 21.
+
+36
+00:01:10,000 --> 00:01:12,000
+It's because.. it will store my name and it
+
+37
+00:01:12,000 --> 00:01:16,000
+will also give me a 16 space extra.
+
+38
+00:01:16,000 --> 00:01:18,000
+Now why it gives me that space is because..
+
+39
+00:01:18,000 --> 00:01:21,000
+Every time we'll change data, and if it consumes
+
+40
+00:01:21,000 --> 00:01:24,000
+a continuous memory location inside your heap memory
+
+41
+00:01:24,000 --> 00:01:26,000
+and what if there's no continuous location next
+
+42
+00:01:26,000 --> 00:01:28,000
+(fumbles).. I mean Th.. what if there is no location
+
+43
+00:01:28,000 --> 00:01:30,000
+available. There's no space available.
+
+44
+00:01:30,000 --> 00:01:32,000
+In that case, it has to relocate. So to
+
+45
+00:01:32,000 --> 00:01:34,000
+reduce the relo.. relocation of the string
+
+46
+00:01:34,000 --> 00:01:37,000
+it gives you a buffer. Okay.
+
+47
+00:01:37,000 --> 00:01:40,000
+So that's the capacity and now we know how it works.
+
+48
+00:01:40,000 --> 00:01:42,000
+We can also print the length of the string and we can
+
+49
+00:01:42,000 --> 00:01:45,000
+say... sb.length. And length is available in
+
+50
+00:01:45,000 --> 00:01:48,000
+normal string as well. So if I compile
+
+51
+00:01:48,000 --> 00:01:50,000
+and run, you can see the length is 5
+
+52
+00:01:50,000 --> 00:01:52,000
+so, length and capacities are 2 different things.
+
+53
+00:01:52,000 --> 00:01:56,000
+Okay, now can I append data?
+
+54
+00:01:56,000 --> 00:01:58,000
+See, the ultimate thing was.. can I change
+
+55
+00:01:58,000 --> 00:02:00,000
+my data, which is "Navin" in this case.
+
+56
+00:02:00,000 --> 00:02:03,000
+The beauty is string buffer will give you
+
+57
+00:02:03,000 --> 00:02:05,000
+a lot of different methods to do that..
+
+58
+00:02:05,000 --> 00:02:06,000
+You can see we have a metho...method called
+
+59
+00:02:06,000 --> 00:02:08,000
+append.. so you can use append
+
+60
+00:02:08,000 --> 00:02:10,000
+and you can append a data which you want to..
+
+61
+00:02:10,000 --> 00:02:13,000
+So lets say I want to append.. "Reddy" here,
+
+62
+00:02:13,000 --> 00:02:14,000
+and of course I want to give a space
+
+63
+00:02:14,000 --> 00:02:17,000
+between "Navin" uhh.. "Navin" and "Reddy".
+
+64
+00:02:17,000 --> 00:02:19,000
+So you can append and you can print the data...
+
+65
+00:02:19,000 --> 00:02:21,000
+So you can print 'sb' as it is..
+
+66
+00:02:21,000 --> 00:02:23,000
+Let's.. uh. First we have to compile the
+
+67
+00:02:23,000 --> 00:02:25,000
+code.. Run. And you can see the code
+
+68
+00:02:25,000 --> 00:02:27,000
+"Navin" "Reddy" it wo.. that works.
+
+69
+00:02:27,000 --> 00:02:30,000
+Next, what if you want to assign string buffer
+
+70
+00:02:30,000 --> 00:02:32,000
+data to string is example if I do that..uh,
+
+71
+00:02:32,000 --> 00:02:35,000
+you can see.. it will... give you a log.
+
+72
+00:02:35,000 --> 00:02:37,000
+It says, type mismatch: cannot convert from
+
+73
+00:02:37,000 --> 00:02:39,000
+string buffer to String.. oo of course
+
+74
+00:02:39,000 --> 00:02:42,000
+right? HTI is of type string, so in that case
+
+75
+00:02:42,000 --> 00:02:45,000
+you can get the string back.. do we have
+
+76
+00:02:45,000 --> 00:02:46,000
+a method for it?
+
+77
+00:02:46,000 --> 00:02:48,000
+Lets see...yes we do have two string
+
+78
+00:02:48,000 --> 00:02:49,000
+we can use that
+
+79
+00:02:49,000 --> 00:02:52,000
+I think that's the only method we can use...
+
+80
+00:02:52,000 --> 00:02:53,000
+Yup, so let's see those two string.
+
+81
+00:02:53,000 --> 00:02:56,000
+So, basically you can use two string to convert
+
+82
+00:02:56,000 --> 00:02:58,000
+the.. . string buffer data. I mean it will
+
+83
+00:02:58,000 --> 00:03:01,000
+get the string format, it was stored in HTR
+
+84
+00:03:01,000 --> 00:03:03,000
+and you can print it.
+
+85
+00:03:03,000 --> 00:03:05,000
+Okay. We can use that... what else we can do
+
+86
+00:03:05,000 --> 00:03:06,000
+with string buffer?
+
+87
+00:03:06,000 --> 00:03:09,000
+If I come back here if I say sb'dot',
+
+88
+00:03:09,000 --> 00:03:11,000
+you can see we have so many methods here.
+
+89
+00:03:11,000 --> 00:03:13,000
+Okay, so we have append.. we have chars, it will give you
+
+90
+00:03:13,000 --> 00:03:17,000
+a character... we have done that
+
+91
+00:03:17,000 --> 00:03:19,000
+okay, so we can also delete something, we can
+
+92
+00:03:19,000 --> 00:03:20,000
+delete a character at an index. So next
+
+93
+00:03:20,000 --> 00:03:23,000
+I will delete a character at location "2".
+
+94
+00:03:23,000 --> 00:03:27,000
+If you try to delete that data..compile and.. run.
+
+95
+00:03:27,000 --> 00:03:29,000
+You can see we got, oh! Something is missing
+
+96
+00:03:29,000 --> 00:03:30,000
+the way is missing there.
+
+97
+00:03:30,000 --> 00:03:33,000
+Because that is at index number "2"
+
+98
+00:03:33,000 --> 00:03:35,000
+okay, so the idea is we basically we can change it
+
+99
+00:03:35,000 --> 00:03:37,000
+and you can experiment it a lot.
+
+100
+00:03:37,000 --> 00:03:41,000
+You can try to use different methods, we can delete,
+
+101
+00:03:41,000 --> 00:03:43,000
+we can insert also in between, lets say
+
+102
+00:03:43,000 --> 00:03:46,000
+I want to insert .. uh. Java at the start,
+
+103
+00:03:46,000 --> 00:03:48,000
+you can do that. So you can say insert
+
+104
+00:03:48,000 --> 00:03:49,000
+you can mention the index value where you want
+
+105
+00:03:49,000 --> 00:03:52,000
+to insert exact location, and the data that you
+
+106
+00:03:52,000 --> 00:03:54,000
+..which you want to insert. So I will say
+
+107
+00:03:54,000 --> 00:03:56,000
+Java 'space', now what it will do is
+
+108
+00:03:56,000 --> 00:04:00,000
+It will add Java at index 0, I mean that is start
+
+109
+00:04:00,000 --> 00:04:02,000
+itself. So if I run, you can see it says Java..
+
+110
+00:04:02,000 --> 00:04:05,000
+Of course you can add Java in between as well.
+
+111
+00:04:05,000 --> 00:04:08,000
+Uh.. lets say I want to add.. after...
+
+112
+00:04:08,000 --> 00:04:10,000
+5th location I think... that should work.
+
+113
+00:04:10,000 --> 00:04:13,000
+After this space it's 6, so let's try that..
+
+114
+00:04:13,000 --> 00:04:15,000
+Compile Run. You can see its.. "Navin"
+
+115
+00:04:15,000 --> 00:04:17,000
+"Java", "Reddy" so it works.
+
+116
+00:04:17,000 --> 00:04:20,000
+Okay.. so, yeah that's how we can basically use insert
+
+117
+00:04:20,000 --> 00:04:22,000
+we have more methods to explore and I would
+
+118
+00:04:22,000 --> 00:04:24,000
+recommend you to do that. Can we just see
+
+119
+00:04:24,000 --> 00:04:26,000
+one more.. We can also get the substring..
+
+120
+00:04:26,000 --> 00:04:27,000
+Let's say if you have a very big string
+
+121
+00:04:27,000 --> 00:04:30,000
+you can specify.. the starting point, ending point
+
+122
+00:04:30,000 --> 00:04:33,000
+using substring. You can set the length as well.
+
+123
+00:04:33,000 --> 00:04:36,000
+So If you set the length of the stream, let's
+
+124
+00:04:36,000 --> 00:04:38,000
+say I want to set the length of "30".
+
+125
+00:04:38,000 --> 00:04:40,000
+So, if you want to add your data and
+
+126
+00:04:40,000 --> 00:04:42,000
+if you want to have a specific length..
+
+127
+00:04:42,000 --> 00:04:43,000
+Which is 30 here.
+
+128
+00:04:43,000 --> 00:04:44,000
+It will save the data which is whatever
+
+129
+00:04:44,000 --> 00:04:46,000
+you have. "Navin" 20 will be stored and
+
+130
+00:04:46,000 --> 00:04:47,000
+all the other values will be... will be
+
+131
+00:04:47,000 --> 00:04:49,000
+null.. let's see. So after "Navin" Reddy" it will
+
+132
+00:04:49,000 --> 00:04:52,000
+add some extra data here... okay.
+
+133
+00:04:52,000 --> 00:04:54,000
+So that you can replace that later. Cool.. we
+
+134
+00:04:54,000 --> 00:04:57,000
+can do that... we can also set a minimum or
+
+135
+00:04:57,000 --> 00:04:59,000
+maximum data. I think there's minimum capacity
+
+136
+00:04:59,000 --> 00:05:02,000
+method which we can use... I think the method
+
+137
+00:05:02,000 --> 00:05:05,000
+name is "ensurecapacity", yeah okay.
+
+138
+00:05:05,000 --> 00:05:08,000
+So we can, we can set the ensurecapacity to 100
+
+139
+00:05:08,000 --> 00:05:11,000
+so it..minimum, minimum capacity will be 100.
+
+140
+00:05:11,000 --> 00:05:13,000
+Okay um that's how you have different methods.
+
+141
+00:05:13,000 --> 00:05:15,000
+Now what's the difference between string buffer and
+
+142
+00:05:15,000 --> 00:05:17,000
+string builder. So as I mentioned we also have
+
+143
+00:05:17,000 --> 00:05:18,000
+string builder right?..there's only one
+
+144
+00:05:18,000 --> 00:05:22,000
+difference, string buffer is thread safe and
+
+145
+00:05:22,000 --> 00:05:23,000
+string builder is not..
+
+146
+00:05:23,000 --> 00:05:25,000
+Now what is thread safe means that we
+
+147
+00:05:25,000 --> 00:05:26,000
+will understand once we talk about
+
+148
+00:05:26,000 --> 00:05:29,000
+thread concept.. so that point also ..
+
+149
+00:05:29,000 --> 00:05:31,000
+we'll talk about difference between string buffer
+
+150
+00:05:31,000 --> 00:05:33,000
+and string builder, but what other methods
+
+151
+00:05:33,000 --> 00:05:35,000
+you have in string buffer is almost
+
+152
+00:05:35,000 --> 00:05:37,000
+the same as string builder. So if you
+
+153
+00:05:37,000 --> 00:05:39,000
+know one.. you know the other one as well.
+
+154
+00:05:39,000 --> 00:05:41,000
+Okay, so that's about string buffer and...
+
+155
+00:05:41,000 --> 00:05:43,000
+Some of the methods of string.
+

02 - Core Java/041 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/041 Static Variable_en.srt

@@ -0,0 +1,700 @@
+1
+00:00:00,000 --> 00:00:03,000
+(gentle music)
+
+2
+00:00:03,000 --> 00:00:06,000
+-: In this video, we'll talk about static keyword.
+
+3
+00:00:06,000 --> 00:00:08,000
+From the start itself, when we have written the first code,
+
+4
+00:00:08,000 --> 00:00:10,000
+we are looking at the static keyword,
+
+5
+00:00:10,000 --> 00:00:12,000
+and the question still remains, right,
+
+6
+00:00:12,000 --> 00:00:14,000
+what is the static?
+
+7
+00:00:14,000 --> 00:00:15,000
+So we know what is method is,
+
+8
+00:00:15,000 --> 00:00:17,000
+we know what is return type, we know what is class.
+
+9
+00:00:17,000 --> 00:00:21,000
+But again, problem gets stuck here in static itself.
+
+10
+00:00:21,000 --> 00:00:23,000
+Now to make you understand this, let's take an example here.
+
+11
+00:00:23,000 --> 00:00:26,000
+So let's say we have an example of mobile phone,
+
+12
+00:00:26,000 --> 00:00:28,000
+and every mobile phone has a brand.
+
+13
+00:00:28,000 --> 00:00:31,000
+So brand will be string, so it's String brand,
+
+14
+00:00:32,000 --> 00:00:34,000
+and we can have a default value for it.
+
+15
+00:00:34,000 --> 00:00:37,000
+We can have int, which is price,
+
+16
+00:00:37,000 --> 00:00:42,000
+and then String network, okay?
+
+17
+00:00:43,000 --> 00:00:46,000
+And we can also make it for a specific brand as well,
+
+18
+00:00:46,000 --> 00:00:47,000
+but let's keep it simple.
+
+19
+00:00:47,000 --> 00:00:49,000
+Let's have a mobile phone, different brands,
+
+20
+00:00:49,000 --> 00:00:53,000
+different price, different network, and we'll say name.
+
+21
+00:00:53,000 --> 00:00:56,000
+Okay, now see name itself of a mobile phone changes, right?
+
+22
+00:00:56,000 --> 00:01:00,000
+So we used to say normal phones, then we got smartphones,
+
+23
+00:01:00,000 --> 00:01:02,000
+and now we have foldable phones, right?
+
+24
+00:01:02,000 --> 00:01:04,000
+So we can have a different name to phones nowadays.
+
+25
+00:01:04,000 --> 00:01:06,000
+Every phone is called a smartphone now
+
+26
+00:01:06,000 --> 00:01:08,000
+because that's what we call it.
+
+27
+00:01:08,000 --> 00:01:09,000
+Usually, we used to call it mobile,
+
+28
+00:01:09,000 --> 00:01:11,000
+then we used to call it phone, right?
+
+29
+00:01:11,000 --> 00:01:13,000
+So we have a name here as well.
+
+30
+00:01:13,000 --> 00:01:16,000
+What do you call a mobile phone? So now it's a smartphone.
+
+31
+00:01:16,000 --> 00:01:18,000
+Okay, so if you want to work with this mobile phone,
+
+32
+00:01:18,000 --> 00:01:19,000
+of course, you have to create an object, right?
+
+33
+00:01:19,000 --> 00:01:21,000
+So if I say Mobile obj,
+
+34
+00:01:21,000 --> 00:01:24,000
+if I will say Mobile obj1 = new Mobile.
+
+35
+00:01:24,000 --> 00:01:26,000
+And of course, every mobile will have
+
+36
+00:01:26,000 --> 00:01:27,000
+a different parameter here.
+
+37
+00:01:27,000 --> 00:01:29,000
+What I will do is I will just remove this network just
+
+38
+00:01:29,000 --> 00:01:32,000
+to keep it simple, we just want three variables here,
+
+39
+00:01:32,000 --> 00:01:35,000
+obj1.brand, I want to set the brand here.
+
+40
+00:01:35,000 --> 00:01:37,000
+Let's say the brand is Apple
+
+41
+00:01:37,000 --> 00:01:39,000
+since I'm using an Apple phone here.
+
+42
+00:01:39,000 --> 00:01:44,000
+And then the price, let's say $1,500.
+
+43
+00:01:44,000 --> 00:01:46,000
+And what else we have? We have a name.
+
+44
+00:01:46,000 --> 00:01:47,000
+So what do you call a mobile phone?
+
+45
+00:01:47,000 --> 00:01:50,000
+So currently, if we talk about Apple phones
+
+46
+00:01:50,000 --> 00:01:54,000
+or any phones nowadays, we call them as a smartphone, okay?
+
+47
+00:01:54,000 --> 00:01:55,000
+I know this variable doesn't make sense,
+
+48
+00:01:55,000 --> 00:01:57,000
+but just for the example,
+
+49
+00:01:57,000 --> 00:02:00,000
+I'm saying name = "SmartPhone", right?
+
+50
+00:02:00,000 --> 00:02:03,000
+Now if you talk about this phone here,
+
+51
+00:02:03,000 --> 00:02:05,000
+we have all these values, right?
+
+52
+00:02:05,000 --> 00:02:09,000
+Now of course, if I create multiple objects,
+
+53
+00:02:09,000 --> 00:02:10,000
+it should have a different value.
+
+54
+00:02:10,000 --> 00:02:11,000
+Of course, every object is different,
+
+55
+00:02:11,000 --> 00:02:13,000
+so we can have a different value to it.
+
+56
+00:02:13,000 --> 00:02:14,000
+If I come back to Apple,
+
+57
+00:02:14,000 --> 00:02:17,000
+let's say the next phone is of Samsung,
+
+58
+00:02:17,000 --> 00:02:20,000
+and the price is let's say $1,700.
+
+59
+00:02:20,000 --> 00:02:24,000
+And then we also call them as SmartPhone, okay?
+
+60
+00:02:24,000 --> 00:02:25,000
+The only thing that we have to change it here
+
+61
+00:02:25,000 --> 00:02:27,000
+as well, obj2, obj2,
+
+62
+00:02:27,000 --> 00:02:30,000
+and then I can print the values as well.
+
+63
+00:02:30,000 --> 00:02:31,000
+You know what I will do?
+
+64
+00:02:31,000 --> 00:02:33,000
+I will just create a method which will print everything.
+
+65
+00:02:33,000 --> 00:02:34,000
+I will say public void show.
+
+66
+00:02:34,000 --> 00:02:36,000
+It should print all the details here.
+
+67
+00:02:36,000 --> 00:02:39,000
+So it should print brand so that I don't have
+
+68
+00:02:39,000 --> 00:02:41,000
+to print that every time,
+
+69
+00:02:41,000 --> 00:02:45,000
+and I will say price, and I will print name as well.
+
+70
+00:02:45,000 --> 00:02:45,000
+Now by doing this,
+
+71
+00:02:45,000 --> 00:02:49,000
+what I'm doing is instead of printing it here every value,
+
+72
+00:02:49,000 --> 00:02:53,000
+I can simply call obj1.show do show and obj2.show.
+
+73
+00:02:53,000 --> 00:02:56,000
+So it'll print its own value, not other values.
+
+74
+00:02:56,000 --> 00:03:00,000
+And if I come back here, compile and run,
+
+75
+00:03:00,000 --> 00:03:01,000
+you can see we got the values, right?
+
+76
+00:03:01,000 --> 00:03:02,000
+Nothing complex here.
+
+77
+00:03:02,000 --> 00:03:05,000
+The thing is if we talk about these variables here,
+
+78
+00:03:05,000 --> 00:03:07,000
+they are called instance variable, right?
+
+79
+00:03:07,000 --> 00:03:08,000
+Now if you create a variable inside a method,
+
+80
+00:03:08,000 --> 00:03:10,000
+that's a local variable.
+
+81
+00:03:10,000 --> 00:03:12,000
+But this are your instance variable,
+
+82
+00:03:12,000 --> 00:03:14,000
+and every variable
+
+83
+00:03:14,000 --> 00:03:16,000
+for a particular object is different, right?
+
+84
+00:03:16,000 --> 00:03:17,000
+The value will be different.
+
+85
+00:03:17,000 --> 00:03:21,000
+Now what I want is I want to have the name
+
+86
+00:03:21,000 --> 00:03:23,000
+to be same for all the objects.
+
+87
+00:03:23,000 --> 00:03:25,000
+See, because what is happening is in your memory,
+
+88
+00:03:25,000 --> 00:03:27,000
+so let's say we have a JVM, a big JVM,
+
+89
+00:03:27,000 --> 00:03:30,000
+and inside this, you have a stack
+
+90
+00:03:30,000 --> 00:03:34,000
+where you have all the reference and locations and address,
+
+91
+00:03:34,000 --> 00:03:35,000
+and then you have a heap memory.
+
+92
+00:03:35,000 --> 00:03:38,000
+So in total, you can see we got two objects, right?
+
+93
+00:03:38,000 --> 00:03:43,000
+One with Mobile obj1 and one is obj2,
+
+94
+00:03:43,000 --> 00:03:45,000
+and then of course, they have the address as well.
+
+95
+00:03:45,000 --> 00:03:47,000
+So this is 101, 103.
+
+96
+00:03:47,000 --> 00:03:51,000
+And of course, this will be 101, 103,
+
+97
+00:03:51,000 --> 00:03:52,000
+and you will be referring that, right?
+
+98
+00:03:52,000 --> 00:03:55,000
+So this is for that here, this is for that here.
+
+99
+00:03:55,000 --> 00:03:57,000
+Now that's how we can basically use it,
+
+100
+00:03:57,000 --> 00:03:59,000
+and every object will have a different value.
+
+101
+00:03:59,000 --> 00:04:01,000
+But what if I want
+
+102
+00:04:01,000 --> 00:04:03,000
+to have a common value for all the objects?
+
+103
+00:04:03,000 --> 00:04:06,000
+The problem with this is if I want to make sure
+
+104
+00:04:06,000 --> 00:04:08,000
+that the name variable should not be a part of the object,
+
+105
+00:04:08,000 --> 00:04:09,000
+because that's an instance variable.
+
+106
+00:04:09,000 --> 00:04:11,000
+Now it will have a part of the object,
+
+107
+00:04:11,000 --> 00:04:13,000
+and every object will have a different value.
+
+108
+00:04:13,000 --> 00:04:17,000
+I want this name to be common for all. How do I do that?
+
+109
+00:04:17,000 --> 00:04:22,000
+Now if you make this variable as static, now by doing that,
+
+110
+00:04:22,000 --> 00:04:26,000
+what we are doing is we are making this name variable common
+
+111
+00:04:26,000 --> 00:04:28,000
+to all the object.
+
+112
+00:04:28,000 --> 00:04:31,000
+What I mean by that is, let's say after sometime,
+
+113
+00:04:31,000 --> 00:04:34,000
+if I say obj1.name.
+
+114
+00:04:34,000 --> 00:04:37,000
+If I change the name to let's say a Phone here,
+
+115
+00:04:37,000 --> 00:04:39,000
+just a Phone, not a SmartPhone anymore.
+
+116
+00:04:39,000 --> 00:04:42,000
+If you make this as a Phone and if you see the values,
+
+117
+00:04:42,000 --> 00:04:46,000
+it will affect all the objects.
+
+118
+00:04:46,000 --> 00:04:49,000
+You can see we are trying to change the name of obj1,
+
+119
+00:04:49,000 --> 00:04:54,000
+but we are actually changing the name of obj2 as well.
+
+120
+00:04:54,000 --> 00:04:56,000
+You can see this is also Phone now.
+
+121
+00:04:56,000 --> 00:04:59,000
+The reason is the static variable is actually shared
+
+122
+00:04:59,000 --> 00:05:01,000
+by all the objects.
+
+123
+00:05:01,000 --> 00:05:03,000
+So basically, we'll not be having individual static variable
+
+124
+00:05:03,000 --> 00:05:05,000
+for every object.
+
+125
+00:05:05,000 --> 00:05:06,000
+We have a common variable,
+
+126
+00:05:06,000 --> 00:05:08,000
+which will be used by all the objects.
+
+127
+00:05:08,000 --> 00:05:11,000
+Imagine there is a common variable here, name,
+
+128
+00:05:11,000 --> 00:05:14,000
+and all the objects will be referring to the same variable.
+
+129
+00:05:14,000 --> 00:05:16,000
+So if you change the value for this,
+
+130
+00:05:16,000 --> 00:05:19,000
+it will affect all the objects, okay?
+
+131
+00:05:19,000 --> 00:05:22,000
+Now this is why we use static.
+
+132
+00:05:22,000 --> 00:05:24,000
+Now the beauty is see,
+
+133
+00:05:24,000 --> 00:05:26,000
+why we have to refer brand with obj1,
+
+134
+00:05:26,000 --> 00:05:27,000
+price with obj1 is
+
+135
+00:05:27,000 --> 00:05:31,000
+because every object will have a different value for it.
+
+136
+00:05:31,000 --> 00:05:34,000
+Now don't you think name is a static variable,
+
+137
+00:05:34,000 --> 00:05:37,000
+and it will be common for all the objects?
+
+138
+00:05:37,000 --> 00:05:40,000
+And that's why you can actually call name
+
+139
+00:05:40,000 --> 00:05:43,000
+with the help of a class name itself.
+
+140
+00:05:43,000 --> 00:05:45,000
+You can simply say Mobile.name.
+
+141
+00:05:45,000 --> 00:05:47,000
+So static variables should be called
+
+142
+00:05:47,000 --> 00:05:50,000
+with their class name, not with objects.
+
+143
+00:05:50,000 --> 00:05:53,000
+You can call with objects, but avoid it.
+
+144
+00:05:53,000 --> 00:05:55,000
+And that's why you can see it gives you warning as well.
+
+145
+00:05:55,000 --> 00:05:58,000
+It says, "The static field Mobile.name should be accessed
+
+146
+00:05:58,000 --> 00:06:03,000
+in a static way," which is using the class name,
+
+147
+00:06:03,000 --> 00:06:05,000
+which is mobile, okay?
+
+148
+00:06:05,000 --> 00:06:06,000
+So the point
+
+149
+00:06:06,000 --> 00:06:09,000
+to remember here is static variables are actually shared
+
+150
+00:06:09,000 --> 00:06:11,000
+by different objects,
+
+151
+00:06:11,000 --> 00:06:13,000
+and if you want to refer to a static variable,
+
+152
+00:06:13,000 --> 00:06:14,000
+you can use a class name.
+
+153
+00:06:14,000 --> 00:06:17,000
+So there's a different area in your JVM
+
+154
+00:06:17,000 --> 00:06:19,000
+where you have all the static variables.
+
+155
+00:06:19,000 --> 00:06:22,000
+And here as well, I should say Mobile.
+
+156
+00:06:22,000 --> 00:06:24,000
+Now the thing is in non-static methods,
+
+157
+00:06:24,000 --> 00:06:26,000
+you can use static variables.
+
+158
+00:06:26,000 --> 00:06:30,000
+There's no harm, okay? And that's a point to remember.
+
+159
+00:06:30,000 --> 00:06:31,000
+In the next video,
+
+160
+00:06:31,000 --> 00:06:33,000
+we'll talk about what if you create a static method?
+
+161
+00:06:33,000 --> 00:06:35,000
+Yes, we can do that. We can create static method.
+
+162
+00:06:35,000 --> 00:06:38,000
+And the question is, can I use instance variables there?
+
+163
+00:06:38,000 --> 00:06:40,000
+Okay, we'll see that in the next video.
+
+164
+00:06:40,000 --> 00:06:44,000
+But here, we talked about what is a static keyword.
+
+165
+00:06:44,000 --> 00:06:47,000
+So static keyword means you are making something
+
+166
+00:06:47,000 --> 00:06:49,000
+as a class member, not a object member.
+
+167
+00:06:49,000 --> 00:06:52,000
+So static, this name here belongs to a class,
+
+168
+00:06:52,000 --> 00:06:53,000
+not to the object,
+
+169
+00:06:53,000 --> 00:06:55,000
+and that's why you were able to use this
+
+170
+00:06:55,000 --> 00:06:58,000
+with the help of a class name, okay?
+
+171
+00:06:58,000 --> 00:07:00,000
+And then you're saving memory as well
+
+172
+00:07:00,000 --> 00:07:03,000
+because not every object will have their own value for it
+
+173
+00:07:03,000 --> 00:07:05,000
+or their own copy for it.
+
+174
+00:07:05,000 --> 00:07:06,000
+So that's about static variable.
+
+175
+00:07:06,000 --> 00:07:09,000
+In the next video, we'll talk about static methods.
+

02 - Core Java/042 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/042 Static method_en.srt

@@ -0,0 +1,508 @@
+1
+00:00:03,000 --> 00:00:05,000
+-: Now once we talked about static variable,
+
+2
+00:00:05,000 --> 00:00:07,000
+it's time to talk about static methods.
+
+3
+00:00:07,000 --> 00:00:08,000
+Now what I will do is
+
+4
+00:00:08,000 --> 00:00:11,000
+I will just try to remove all this content from here
+
+5
+00:00:11,000 --> 00:00:13,000
+just to keep it simple
+
+6
+00:00:13,000 --> 00:00:16,000
+and let's make a static method.
+
+7
+00:00:16,000 --> 00:00:17,000
+Now, the method which we have here show
+
+8
+00:00:17,000 --> 00:00:19,000
+is not a static method, right?
+
+9
+00:00:19,000 --> 00:00:20,000
+It's a instance method,
+
+10
+00:00:20,000 --> 00:00:23,000
+is because we have not mentioned a static keyword.
+
+11
+00:00:23,000 --> 00:00:27,000
+Now, whenever you want to work with a non-static method,
+
+12
+00:00:27,000 --> 00:00:29,000
+you need to create an object of it.
+
+13
+00:00:29,000 --> 00:00:30,000
+Of course, if you want to call,
+
+14
+00:00:30,000 --> 00:00:33,000
+you have to create object of mobile.
+
+15
+00:00:33,000 --> 00:00:36,000
+In fact, you know, actually we need those objects here
+
+16
+00:00:36,000 --> 00:00:40,000
+and let's keep it here just to use it.
+
+17
+00:00:40,000 --> 00:00:42,000
+Now let me create a simple static method.
+
+18
+00:00:42,000 --> 00:00:47,000
+So I will say public static void show1.
+
+19
+00:00:48,000 --> 00:00:49,000
+Again, if you can see,
+
+20
+00:00:49,000 --> 00:00:52,000
+I'm using a different method name just to differentiate it.
+
+21
+00:00:52,000 --> 00:00:54,000
+And here, if I try to,
+
+22
+00:00:54,000 --> 00:00:58,000
+first of all, I will just print in static method.
+
+23
+00:00:59,000 --> 00:01:01,000
+Now, how do we call the static method?
+
+24
+00:01:01,000 --> 00:01:04,000
+To call show, we have to get object, right?
+
+25
+00:01:04,000 --> 00:01:08,000
+You can't simply come back here and say, mobile.show,
+
+26
+00:01:08,000 --> 00:01:09,000
+this will not work.
+
+27
+00:01:09,000 --> 00:01:11,000
+If you try to call mobile.show,
+
+28
+00:01:11,000 --> 00:01:12,000
+it'll give you an error.
+
+29
+00:01:12,000 --> 00:01:13,000
+It says,
+
+30
+00:01:13,000 --> 00:01:14,000
+let's see the error.
+
+31
+00:01:14,000 --> 00:01:15,000
+It says cannot make a static reference
+
+32
+00:01:15,000 --> 00:01:17,000
+to a non-static method.
+
+33
+00:01:17,000 --> 00:01:19,000
+That means you cannot call a non-static method
+
+34
+00:01:19,000 --> 00:01:20,000
+with the help of a class name.
+
+35
+00:01:20,000 --> 00:01:23,000
+And that's why you need object here, which you can see.
+
+36
+00:01:23,000 --> 00:01:24,000
+We are using obj1, obj2 .
+
+37
+00:01:25,000 --> 00:01:28,000
+But can I call show one from mobile?
+
+38
+00:01:28,000 --> 00:01:29,000
+Let's try, and we can.
+
+39
+00:01:29,000 --> 00:01:32,000
+You can see that there's no problem.
+
+40
+00:01:32,000 --> 00:01:34,000
+So you can call a static method
+
+41
+00:01:34,000 --> 00:01:36,000
+directly with the help of a class name.
+
+42
+00:01:36,000 --> 00:01:37,000
+That's what we are doing here.
+
+43
+00:01:37,000 --> 00:01:39,000
+We're directly calling it with a class name.
+
+44
+00:01:39,000 --> 00:01:41,000
+Now the question is,
+
+45
+00:01:41,000 --> 00:01:41,000
+this looks cool, right?
+
+46
+00:01:41,000 --> 00:01:44,000
+Static method can be used directly with a class name,
+
+47
+00:01:44,000 --> 00:01:46,000
+but can I use a variables here?
+
+48
+00:01:46,000 --> 00:01:48,000
+Let's try to do the same thing.
+
+49
+00:01:48,000 --> 00:01:51,000
+I will just copy this line and paste it here.
+
+50
+00:01:51,000 --> 00:01:52,000
+Let's see what happens.
+
+51
+00:01:52,000 --> 00:01:54,000
+The moment you do that,
+
+52
+00:01:54,000 --> 00:01:55,000
+you can say there's no problem with name.
+
+53
+00:01:55,000 --> 00:01:58,000
+So that means you can use a static variable
+
+54
+00:01:58,000 --> 00:02:00,000
+inside a static method,
+
+55
+00:02:00,000 --> 00:02:03,000
+but you cannot use a non-static variable
+
+56
+00:02:03,000 --> 00:02:06,000
+inside a static method.
+
+57
+00:02:06,000 --> 00:02:08,000
+The question is why?
+
+58
+00:02:08,000 --> 00:02:10,000
+I mean, think about this,
+
+59
+00:02:10,000 --> 00:02:12,000
+brand and price they instance variable.
+
+60
+00:02:12,000 --> 00:02:14,000
+That means it'll be different for different objects.
+
+61
+00:02:14,000 --> 00:02:16,000
+Now, when you call show with obj1,
+
+62
+00:02:16,000 --> 00:02:17,000
+we know that in this show
+
+63
+00:02:17,000 --> 00:02:19,000
+when you are printing brand and price,
+
+64
+00:02:19,000 --> 00:02:21,000
+you're talking about obj1.
+
+65
+00:02:21,000 --> 00:02:23,000
+When you call show with obj2,
+
+66
+00:02:23,000 --> 00:02:27,000
+you know that the brand and price will be of obj2.
+
+67
+00:02:27,000 --> 00:02:29,000
+But then when you call mobile.show1,
+
+68
+00:02:29,000 --> 00:02:33,000
+how do we know which object you're referring to?
+
+69
+00:02:33,000 --> 00:02:36,000
+So this brand belongs to obj1 or it belongs to obj2
+
+70
+00:02:36,000 --> 00:02:37,000
+and that's why it says,
+
+71
+00:02:37,000 --> 00:02:39,000
+hey, there's a confusion, right?
+
+72
+00:02:39,000 --> 00:02:40,000
+Let's not do that.
+
+73
+00:02:40,000 --> 00:02:42,000
+Let's not have a non-static variable
+
+74
+00:02:42,000 --> 00:02:45,000
+directly getting access in a static method.
+
+75
+00:02:45,000 --> 00:02:46,000
+It's not possible.
+
+76
+00:02:46,000 --> 00:02:48,000
+This time I added a directly keyword that
+
+77
+00:02:48,000 --> 00:02:50,000
+that means indirectly is possible.
+
+78
+00:02:50,000 --> 00:02:51,000
+Now, how will you do the indirectly?
+
+79
+00:02:51,000 --> 00:02:52,000
+It's very simple.
+
+80
+00:02:52,000 --> 00:02:56,000
+What if you can actually pass the object itself?
+
+81
+00:02:56,000 --> 00:02:57,000
+You can say,
+
+82
+00:02:57,000 --> 00:03:00,000
+hey, I want to run show 1 for obj1 object.
+
+83
+00:03:01,000 --> 00:03:02,000
+Now, since you are passing the object,
+
+84
+00:03:02,000 --> 00:03:04,000
+you have to also accept it here.
+
+85
+00:03:04,000 --> 00:03:07,000
+So it can say mobile obj.
+
+86
+00:03:07,000 --> 00:03:10,000
+And now, now since we have the object,
+
+87
+00:03:10,000 --> 00:03:13,000
+I can refer that with the help of obj1.brand,
+
+88
+00:03:13,000 --> 00:03:16,000
+I mean, obj.brand on obj.prize.
+
+89
+00:03:16,000 --> 00:03:19,000
+So basically we cannot directly use a non-static variable
+
+90
+00:03:19,000 --> 00:03:21,000
+inside a static method.
+
+91
+00:03:21,000 --> 00:03:23,000
+But if you have object reference, then you can use it.
+
+92
+00:03:23,000 --> 00:03:25,000
+Because now we can differentiate.
+
+93
+00:03:25,000 --> 00:03:26,000
+So the brand which I'm talking about
+
+94
+00:03:26,000 --> 00:03:28,000
+is for obj1, not for obj2.
+
+95
+00:03:28,000 --> 00:03:29,000
+So that's how we have to do it.
+
+96
+00:03:29,000 --> 00:03:31,000
+So that's how we work with static method.
+
+97
+00:03:31,000 --> 00:03:33,000
+Now, if you observe here,
+
+98
+00:03:33,000 --> 00:03:34,000
+from start we are using this, right?
+
+99
+00:03:34,000 --> 00:03:37,000
+The main method is static.
+
+100
+00:03:37,000 --> 00:03:39,000
+Why in this world we have a main static?
+
+101
+00:03:39,000 --> 00:03:42,000
+Is because if you don't make main static,
+
+102
+00:03:42,000 --> 00:03:43,000
+if this was a syntax,
+
+103
+00:03:43,000 --> 00:03:46,000
+the problem is if you don't mention static,
+
+104
+00:03:46,000 --> 00:03:50,000
+that means main becomes a non-static method,
+
+105
+00:03:50,000 --> 00:03:53,000
+which means if you want to call main,
+
+106
+00:03:53,000 --> 00:03:55,000
+we have to first create the object of demo.
+
+107
+00:03:55,000 --> 00:03:57,000
+Oh, that means you cannot call main
+
+108
+00:03:57,000 --> 00:03:59,000
+without the object of demo.
+
+109
+00:03:59,000 --> 00:04:01,000
+But the question is, we all know
+
+110
+00:04:01,000 --> 00:04:04,000
+that main is a starting point of execution.
+
+111
+00:04:04,000 --> 00:04:07,000
+If the execution has not started,
+
+112
+00:04:07,000 --> 00:04:08,000
+how can you create object of demo?
+
+113
+00:04:08,000 --> 00:04:11,000
+Okay, so if there's a deadlock here, right?
+
+114
+00:04:11,000 --> 00:04:13,000
+So to solve that problem, what we can do is
+
+115
+00:04:13,000 --> 00:04:15,000
+we can make this variable as static.
+
+116
+00:04:15,000 --> 00:04:17,000
+The moment you do that, we are saying,
+
+117
+00:04:17,000 --> 00:04:18,000
+hey, you know what?
+
+118
+00:04:18,000 --> 00:04:22,000
+To call main we don't need object of demo.
+
+119
+00:04:22,000 --> 00:04:24,000
+Problem solved, right?
+
+120
+00:04:24,000 --> 00:04:26,000
+So yeah, this is how we can solve this problem
+
+121
+00:04:26,000 --> 00:04:30,000
+and this is what static methods are.
+
+122
+00:04:30,000 --> 00:04:31,000
+Anything else?
+
+123
+00:04:31,000 --> 00:04:33,000
+Actually, I think we, it looks good.
+
+124
+00:04:33,000 --> 00:04:35,000
+In the next video, let's try to see
+
+125
+00:04:35,000 --> 00:04:37,000
+something more about static.
+
+126
+00:04:37,000 --> 00:04:39,000
+There's a concept of static block,
+
+127
+00:04:39,000 --> 00:04:41,000
+which we'll discuss in the next video.
+

02 - Core Java/043 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/043 Static block_en.srt

@@ -0,0 +1,800 @@
+1
+00:00:00,000 --> 00:00:03,000
+(gentle piano music)
+
+2
+00:00:03,000 --> 00:00:05,000
+-: Now we know what is static variables,
+
+3
+00:00:05,000 --> 00:00:06,000
+static methods, right?
+
+4
+00:00:06,000 --> 00:00:08,000
+Now let's try to expand this more.
+
+5
+00:00:08,000 --> 00:00:09,000
+To simplify this,
+
+6
+00:00:09,000 --> 00:00:10,000
+what I will do is I will remove the static method
+
+7
+00:00:10,000 --> 00:00:11,000
+for some time
+
+8
+00:00:11,000 --> 00:00:14,000
+and I will also decrease this code.
+
+9
+00:00:14,000 --> 00:00:16,000
+Let's only work with one object now.
+
+10
+00:00:16,000 --> 00:00:20,000
+And here, see, normally when you work with variables,
+
+11
+00:00:20,000 --> 00:00:23,000
+so we know that this is an instance variable,
+
+12
+00:00:23,000 --> 00:00:26,000
+and this is a static variable, right, the name.
+
+13
+00:00:26,000 --> 00:00:29,000
+Now to instantiate the instance variable,
+
+14
+00:00:29,000 --> 00:00:29,000
+what do we do?
+
+15
+00:00:29,000 --> 00:00:33,000
+Of course we can instantiate the variables from here,
+
+16
+00:00:33,000 --> 00:00:34,000
+but then what if you want
+
+17
+00:00:34,000 --> 00:00:36,000
+to instantiate the variable on this line,
+
+18
+00:00:36,000 --> 00:00:37,000
+if you want to give some value?
+
+19
+00:00:37,000 --> 00:00:39,000
+Not instantiate, if you want to initialize the variable,
+
+20
+00:00:39,000 --> 00:00:40,000
+what you will do?
+
+21
+00:00:40,000 --> 00:00:42,000
+So basically we have seen one concept,
+
+22
+00:00:42,000 --> 00:00:43,000
+right, which is constructor.
+
+23
+00:00:43,000 --> 00:00:48,000
+So using constructor, we can say, okay, public Mobile,
+
+24
+00:00:49,000 --> 00:00:51,000
+and we can give some default values to it, right?
+
+25
+00:00:51,000 --> 00:00:53,000
+So by default, the brand will be empty string,
+
+26
+00:00:53,000 --> 00:00:55,000
+and by default the price will be,
+
+27
+00:00:55,000 --> 00:00:57,000
+let's say $200, right?
+
+28
+00:00:57,000 --> 00:01:01,000
+So this is the default brand, default text,
+
+29
+00:01:01,000 --> 00:01:02,000
+and default number, right?
+
+30
+00:01:02,000 --> 00:01:03,000
+Which we want to give.
+
+31
+00:01:03,000 --> 00:01:04,000
+What about name?
+
+32
+00:01:04,000 --> 00:01:06,000
+I can also give a default name to a name,
+
+33
+00:01:06,000 --> 00:01:09,000
+which is phone in this case, let's say.
+
+34
+00:01:09,000 --> 00:01:10,000
+And we can do that.
+
+35
+00:01:10,000 --> 00:01:12,000
+We can initialize the static variable
+
+36
+00:01:12,000 --> 00:01:13,000
+inside a constructor,
+
+37
+00:01:13,000 --> 00:01:14,000
+and there's no harm in that.
+
+38
+00:01:14,000 --> 00:01:19,000
+Now the problem is every time you create an object,
+
+39
+00:01:19,000 --> 00:01:20,000
+every time you create one more object,
+
+40
+00:01:20,000 --> 00:01:22,000
+it'll call the construct, right?
+
+41
+00:01:22,000 --> 00:01:24,000
+And don't you think it makes sense for this tool
+
+42
+00:01:24,000 --> 00:01:26,000
+to initialize every time,
+
+43
+00:01:26,000 --> 00:01:29,000
+but why name has to initialize every time?
+
+44
+00:01:29,000 --> 00:01:32,000
+I feel that the name variable, which is static,
+
+45
+00:01:32,000 --> 00:01:34,000
+should be initialized only once.
+
+46
+00:01:34,000 --> 00:01:34,000
+What do you feel?
+
+47
+00:01:34,000 --> 00:01:36,000
+Of course the same thing, right?
+
+48
+00:01:36,000 --> 00:01:37,000
+How will you do that?
+
+49
+00:01:37,000 --> 00:01:38,000
+So if you mention that here,
+
+50
+00:01:38,000 --> 00:01:40,000
+of course every time you call the constructor,
+
+51
+00:01:40,000 --> 00:01:41,000
+it will initialize.
+
+52
+00:01:41,000 --> 00:01:42,000
+We don't wanna do that.
+
+53
+00:01:42,000 --> 00:01:43,000
+Now to achieve that,
+
+54
+00:01:43,000 --> 00:01:47,000
+we have a special block called a static block.
+
+55
+00:01:47,000 --> 00:01:48,000
+Now, in the static block,
+
+56
+00:01:48,000 --> 00:01:52,000
+we can basically initialize the variable,
+
+57
+00:01:52,000 --> 00:01:53,000
+the static variable.
+
+58
+00:01:53,000 --> 00:01:54,000
+Now the good thing
+
+59
+00:01:54,000 --> 00:01:57,000
+about this is the static block will be called only once.
+
+60
+00:01:57,000 --> 00:02:00,000
+Irrespective how many objects you create,
+
+61
+00:02:00,000 --> 00:02:02,000
+it'll call the static block only once.
+
+62
+00:02:02,000 --> 00:02:04,000
+So what I will do is just to demonstrate
+
+63
+00:02:04,000 --> 00:02:08,000
+that I will create one more object here, let's say.
+
+64
+00:02:08,000 --> 00:02:09,000
+And I will not assign any value to it,
+
+65
+00:02:09,000 --> 00:02:14,000
+just to default values obj2, second object.
+
+66
+00:02:14,000 --> 00:02:16,000
+So it'll call the constructor two times.
+
+67
+00:02:16,000 --> 00:02:19,000
+It'll call the static block only once.
+
+68
+00:02:19,000 --> 00:02:19,000
+To prove that,
+
+69
+00:02:19,000 --> 00:02:21,000
+what I will do is I will just print something.
+
+70
+00:02:21,000 --> 00:02:24,000
+I will say in static block.
+
+71
+00:02:24,000 --> 00:02:25,000
+Now the syntax for static block is very simple.
+
+72
+00:02:25,000 --> 00:02:27,000
+It's static keyword,
+
+73
+00:02:27,000 --> 00:02:29,000
+and then you just open and close.
+
+74
+00:02:29,000 --> 00:02:30,000
+There's no bracket or something.
+
+75
+00:02:30,000 --> 00:02:33,000
+It's just a simple block, okay?
+
+76
+00:02:33,000 --> 00:02:33,000
+And in the constructor as well,
+
+77
+00:02:33,000 --> 00:02:38,000
+I will say in constructor, okay?
+
+78
+00:02:38,000 --> 00:02:42,000
+And now with this, let me just compile this code, okay?
+
+79
+00:02:42,000 --> 00:02:43,000
+There is an issue.
+
+80
+00:02:43,000 --> 00:02:45,000
+I have returned one extra, okay.
+
+81
+00:02:45,000 --> 00:02:49,000
+I have removed the curly brackets from here.
+
+82
+00:02:49,000 --> 00:02:52,000
+So compile and run.
+
+83
+00:02:52,000 --> 00:02:54,000
+So you can see it is calling the static block only once,
+
+84
+00:02:54,000 --> 00:02:57,000
+and it's calling constructor two times.
+
+85
+00:02:57,000 --> 00:02:58,000
+There's one more issue,
+
+86
+00:02:58,000 --> 00:03:01,000
+why static block is called first
+
+87
+00:03:01,000 --> 00:03:03,000
+even before the constructor is calling static block.
+
+88
+00:03:03,000 --> 00:03:04,000
+And that's weird.
+
+89
+00:03:04,000 --> 00:03:05,000
+Is it the sequence?
+
+90
+00:03:05,000 --> 00:03:07,000
+Let's try, let me just put this
+
+91
+00:03:07,000 --> 00:03:09,000
+after the constructor.
+
+92
+00:03:09,000 --> 00:03:11,000
+Let's see if it doesn't make any sense.
+
+93
+00:03:11,000 --> 00:03:13,000
+Anyway, Java does not follow the sequence.
+
+94
+00:03:13,000 --> 00:03:16,000
+But just to confirm,
+
+95
+00:03:16,000 --> 00:03:20,000
+you can see the static block is still getting called first.
+
+96
+00:03:20,000 --> 00:03:23,000
+Now to understand that, let's go to the diagram here.
+
+97
+00:03:23,000 --> 00:03:24,000
+See what happens.
+
+98
+00:03:24,000 --> 00:03:26,000
+There are two words,
+
+99
+00:03:26,000 --> 00:03:27,000
+and we only focus on one word.
+
+100
+00:03:27,000 --> 00:03:30,000
+Every time you get the object, that two steps,
+
+101
+00:03:30,000 --> 00:03:34,000
+one, your class loads,
+
+102
+00:03:35,000 --> 00:03:39,000
+and then your objects are, okay,
+
+103
+00:03:39,000 --> 00:03:40,000
+so first your class loads
+
+104
+00:03:40,000 --> 00:03:42,000
+and then your object gets instantiated.
+
+105
+00:03:42,000 --> 00:03:44,000
+So there are two steps.
+
+106
+00:03:44,000 --> 00:03:46,000
+Every time you create the object,
+
+107
+00:03:46,000 --> 00:03:48,000
+there are two steps, class loads
+
+108
+00:03:48,000 --> 00:03:50,000
+and object will then will get initialized.
+
+109
+00:03:50,000 --> 00:03:53,000
+The thing is, the class will load only once.
+
+110
+00:03:53,000 --> 00:03:57,000
+So basically in your JVM, you have a special area here,
+
+111
+00:03:57,000 --> 00:04:00,000
+which is called a class loader, okay?
+
+112
+00:04:00,000 --> 00:04:03,000
+And this will have all the class which are loaded.
+
+113
+00:04:03,000 --> 00:04:04,000
+And by default, of course you don't have
+
+114
+00:04:04,000 --> 00:04:05,000
+any class loaded, right?
+
+115
+00:04:05,000 --> 00:04:09,000
+So the class will get loaded from your library
+
+116
+00:04:09,000 --> 00:04:11,000
+to the class loader.
+
+117
+00:04:11,000 --> 00:04:13,000
+And it'll happen only once.
+
+118
+00:04:13,000 --> 00:04:15,000
+So for the first object, when it sees, "Hey,
+
+119
+00:04:15,000 --> 00:04:18,000
+this object creation, it'll load the class first,"
+
+120
+00:04:18,000 --> 00:04:20,000
+and then it'll create the object.
+
+121
+00:04:20,000 --> 00:04:22,000
+Now, every time you load a class,
+
+122
+00:04:22,000 --> 00:04:25,000
+it'll call the static block.
+
+123
+00:04:25,000 --> 00:04:27,000
+Now, since class loading happens first,
+
+124
+00:04:27,000 --> 00:04:29,000
+and that's why it'll call the static block first,
+
+125
+00:04:29,000 --> 00:04:31,000
+and then it'll create the object.
+
+126
+00:04:31,000 --> 00:04:34,000
+And that's why it'll call the constructor
+
+127
+00:04:34,000 --> 00:04:36,000
+after static block.
+
+128
+00:04:36,000 --> 00:04:38,000
+Now, irrespective of how many objects you create,
+
+129
+00:04:38,000 --> 00:04:40,000
+the class is already loaded, right?
+
+130
+00:04:40,000 --> 00:04:42,000
+So you can simply create the next object
+
+131
+00:04:42,000 --> 00:04:43,000
+without loading because it's already loaded.
+
+132
+00:04:43,000 --> 00:04:46,000
+Now my question is, if that is how it is working,
+
+133
+00:04:46,000 --> 00:04:48,000
+what if I don't create any object?
+
+134
+00:04:48,000 --> 00:04:50,000
+I'm not getting any object now.
+
+135
+00:04:50,000 --> 00:04:52,000
+So if you don't create the object,
+
+136
+00:04:52,000 --> 00:04:54,000
+of course it'll not call the constructor.
+
+137
+00:04:54,000 --> 00:04:55,000
+But what about static block?
+
+138
+00:04:55,000 --> 00:04:57,000
+It'll not even call the static block.
+
+139
+00:04:57,000 --> 00:05:00,000
+If you can see, we don't have any output, oh, okay.
+
+140
+00:05:00,000 --> 00:05:02,000
+So that means if you don't create the object,
+
+141
+00:05:02,000 --> 00:05:05,000
+it'll not load the class as well.
+
+142
+00:05:05,000 --> 00:05:06,000
+But what if you wanna do that?
+
+143
+00:05:06,000 --> 00:05:10,000
+What if you want to load the class?
+
+144
+00:05:10,000 --> 00:05:11,000
+How would you do that?
+
+145
+00:05:11,000 --> 00:05:14,000
+Now for that, we have a special class inside Java,
+
+146
+00:05:14,000 --> 00:05:16,000
+which is called a Class class.
+
+147
+00:05:16,000 --> 00:05:17,000
+Yeah, that's a class.
+
+148
+00:05:17,000 --> 00:05:20,000
+Okay, I know Java has been weird.
+
+149
+00:05:20,000 --> 00:05:22,000
+We have Object class, we have Class class,
+
+150
+00:05:22,000 --> 00:05:23,000
+but that's how it is designed.
+
+151
+00:05:23,000 --> 00:05:26,000
+So Java Class, if you go there,
+
+152
+00:05:26,000 --> 00:05:29,000
+you can see it's a class and it has a lot of methods to it.
+
+153
+00:05:29,000 --> 00:05:32,000
+One of the methods which we want to use here is forName.
+
+154
+00:05:32,000 --> 00:05:36,000
+Now forName is a method which does one thing
+
+155
+00:05:36,000 --> 00:05:38,000
+which loads your class.
+
+156
+00:05:38,000 --> 00:05:40,000
+And you just have to mention your class name.
+
+157
+00:05:40,000 --> 00:05:41,000
+What's the class name?
+
+158
+00:05:41,000 --> 00:05:43,000
+Well, the class name is Mobile.
+
+159
+00:05:43,000 --> 00:05:44,000
+So in this you can mention the class name.
+
+160
+00:05:44,000 --> 00:05:46,000
+That's it, okay?
+
+161
+00:05:46,000 --> 00:05:48,000
+The only problem is it throws an exception, okay?
+
+162
+00:05:48,000 --> 00:05:50,000
+At this point we have not talked about exception,
+
+163
+00:05:50,000 --> 00:05:52,000
+but just ignore this line.
+
+164
+00:05:52,000 --> 00:05:55,000
+We'll talk about this in detail later once we start
+
+165
+00:05:55,000 --> 00:05:56,000
+with the exception concept.
+
+166
+00:05:56,000 --> 00:05:58,000
+But as of now, just to make it work,
+
+167
+00:05:58,000 --> 00:06:00,000
+I'm just writing this line, ignore it.
+
+168
+00:06:00,000 --> 00:06:04,000
+What's important is the class.forName will load your class.
+
+169
+00:06:04,000 --> 00:06:07,000
+If I go to forName, you can see forName is a method,
+
+170
+00:06:07,000 --> 00:06:08,000
+and it's a static method.
+
+171
+00:06:08,000 --> 00:06:11,000
+So you can call this with a class name.
+
+172
+00:06:12,000 --> 00:06:14,000
+And this particular method,
+
+173
+00:06:15,000 --> 00:06:18,000
+do they have any definition mentioned?
+
+174
+00:06:18,000 --> 00:06:20,000
+Okay, so it says the system class loader is used.
+
+175
+00:06:20,000 --> 00:06:23,000
+So basically it'll load the system class loader
+
+176
+00:06:23,000 --> 00:06:26,000
+to load this class.
+
+177
+00:06:26,000 --> 00:06:28,000
+Okay, so which class, Mobile class.
+
+178
+00:06:28,000 --> 00:06:31,000
+Okay, so now if I just write this line,
+
+179
+00:06:31,000 --> 00:06:32,000
+it'll not create the object,
+
+180
+00:06:32,000 --> 00:06:36,000
+it'll just instantiate it, compile, run.
+
+181
+00:06:36,000 --> 00:06:40,000
+You can see it says a new static block.
+
+182
+00:06:40,000 --> 00:06:42,000
+Okay, that means you're just loading the class.
+
+183
+00:06:42,000 --> 00:06:44,000
+So basically that's how you load your class.
+
+184
+00:06:44,000 --> 00:06:49,000
+You can simply use this line to load your class.
+
+185
+00:06:49,000 --> 00:06:50,000
+Normally when you build a project,
+
+186
+00:06:50,000 --> 00:06:51,000
+you don't actually use this feature.
+
+187
+00:06:51,000 --> 00:06:53,000
+Yes, there are some situation where you use it.
+
+188
+00:06:53,000 --> 00:06:57,000
+Example, when we start with JDBC, we'll talk about this one,
+
+189
+00:06:57,000 --> 00:06:59,000
+but we normally don't use it.
+
+190
+00:06:59,000 --> 00:07:00,000
+I'm just using this just to show you how
+
+191
+00:07:00,000 --> 00:07:02,000
+to call a static block,
+
+192
+00:07:02,000 --> 00:07:03,000
+how to load a class.
+
+193
+00:07:03,000 --> 00:07:05,000
+Okay, I hope this video makes sense
+
+194
+00:07:05,000 --> 00:07:07,000
+where we talked about static block.
+
+195
+00:07:07,000 --> 00:07:11,000
+So static block is used to initialize the static variables.
+
+196
+00:07:11,000 --> 00:07:12,000
+So that's it from this video in which we talked
+
+197
+00:07:12,000 --> 00:07:14,000
+about static block.
+
+198
+00:07:14,000 --> 00:07:16,000
+In the other videos we have talked about static keyword,
+
+199
+00:07:16,000 --> 00:07:18,000
+static variables, static methods,
+
+200
+00:07:18,000 --> 00:07:19,000
+and yeah, that's about static.
+

02 - Core Java/044 Encapsulation_en.srt

@@ -0,0 +1,1144 @@
+1
+00:00:00,000 --> 00:00:03,000
+(soft music plays)
+
+2
+00:00:03,000 --> 00:00:05,000
+-: In this video, let's talk about Encapsulation.
+
+3
+00:00:05,000 --> 00:00:07,000
+Now I know that's a new term,
+
+4
+00:00:07,000 --> 00:00:09,000
+but when we started with OOPs concept,
+
+5
+00:00:09,000 --> 00:00:12,000
+now Encapsulation is a part of OOPs.
+
+6
+00:00:12,000 --> 00:00:16,000
+So when I say let's implement Object Oriented Programming,
+
+7
+00:00:16,000 --> 00:00:18,000
+so yeah, we have talked about class,
+
+8
+00:00:18,000 --> 00:00:19,000
+we have talked about objects,
+
+9
+00:00:19,000 --> 00:00:21,000
+and the next step is Encapsulation here.
+
+10
+00:00:21,000 --> 00:00:24,000
+Now by word, what Encapsulation means?
+
+11
+00:00:24,000 --> 00:00:25,000
+We have the concept of capsules
+
+12
+00:00:25,000 --> 00:00:28,000
+where we have medicine powder there?
+
+13
+00:00:28,000 --> 00:00:30,000
+So basically we can imagine capsule
+
+14
+00:00:30,000 --> 00:00:34,000
+as something which is keeping it closed, keeping it tight,
+
+15
+00:00:34,000 --> 00:00:37,000
+and no one from the outside world can use it.
+
+16
+00:00:37,000 --> 00:00:39,000
+That makes sense, right?
+
+17
+00:00:39,000 --> 00:00:41,000
+So what we can do here is let's say,
+
+18
+00:00:41,000 --> 00:00:42,000
+let's design a class, okay?
+
+19
+00:00:42,000 --> 00:00:44,000
+And let's name this class as Human.
+
+20
+00:00:44,000 --> 00:00:46,000
+I know we can use different names,
+
+21
+00:00:46,000 --> 00:00:47,000
+but let's go with Human here.
+
+22
+00:00:47,000 --> 00:00:51,000
+And I know we are aliens, but let's say this is Human.
+
+23
+00:00:51,000 --> 00:00:54,000
+Now here, when you have this Human class,
+
+24
+00:00:54,000 --> 00:00:56,000
+a Human will have some parameters, right?
+
+25
+00:00:56,000 --> 00:00:59,000
+Example, if you remember, we have talked about this
+
+26
+00:00:59,000 --> 00:01:01,000
+before, as a Human or as a person,
+
+27
+00:01:01,000 --> 00:01:03,000
+we know a lot of different stuff.
+
+28
+00:01:03,000 --> 00:01:05,000
+So in your mind you have a lot of different concepts
+
+29
+00:01:05,000 --> 00:01:07,000
+or you know a lot of things.
+
+30
+00:01:07,000 --> 00:01:11,000
+Example, you know your name, you know where you stay,
+
+31
+00:01:11,000 --> 00:01:12,000
+you know your favorite actor,
+
+32
+00:01:12,000 --> 00:01:14,000
+you know your favorite trainer.
+
+33
+00:01:14,000 --> 00:01:16,000
+Of course you can name, you can use my name there,
+
+34
+00:01:16,000 --> 00:01:18,000
+but just kidding.
+
+35
+00:01:18,000 --> 00:01:20,000
+So we have different information, right?
+
+36
+00:01:20,000 --> 00:01:21,000
+Now, can you imagine this,
+
+37
+00:01:21,000 --> 00:01:25,000
+that all the information are actually stored in your brain
+
+38
+00:01:25,000 --> 00:01:27,000
+as a variable box?
+
+39
+00:01:27,000 --> 00:01:30,000
+I'm a big fan of Pixel movie, which is,
+
+40
+00:01:30,000 --> 00:01:32,000
+I don't know the exact movie name,
+
+41
+00:01:32,000 --> 00:01:34,000
+but you know, Pac-Man basically eats people
+
+42
+00:01:34,000 --> 00:01:36,000
+and then they become pixels.
+
+43
+00:01:36,000 --> 00:01:40,000
+So you can imagine the data in your mind is cube, okay?
+
+44
+00:01:40,000 --> 00:01:42,000
+And in that box, you have the data.
+
+45
+00:01:42,000 --> 00:01:46,000
+Example, your name is stored in a box, which name Navin,
+
+46
+00:01:46,000 --> 00:01:48,000
+or which name is equal to
+
+47
+00:01:48,000 --> 00:01:50,000
+and in the box will be having a value.
+
+48
+00:01:50,000 --> 00:01:51,000
+For me it's Navin.
+
+49
+00:01:51,000 --> 00:01:53,000
+Let's say, your favorite actor,
+
+50
+00:01:53,000 --> 00:01:56,000
+so you'll be having my favorite actor,
+
+51
+00:01:56,000 --> 00:01:58,000
+and inside the box will be having a value.
+
+52
+00:01:58,000 --> 00:02:02,000
+So what I'm saying is, all the data is stored in your brain
+
+53
+00:02:02,000 --> 00:02:04,000
+in the format of boxes, variables.
+
+54
+00:02:04,000 --> 00:02:07,000
+Now of course you can use these variables, right?
+
+55
+00:02:07,000 --> 00:02:08,000
+So let's say my name is Navin,
+
+56
+00:02:08,000 --> 00:02:10,000
+and let's say if I'm walking on a street
+
+57
+00:02:10,000 --> 00:02:14,000
+and if somebody is asking my name, I might provide my name.
+
+58
+00:02:14,000 --> 00:02:17,000
+What if somebody is asking my email address?
+
+59
+00:02:17,000 --> 00:02:19,000
+I might provide them my email address depending
+
+60
+00:02:19,000 --> 00:02:20,000
+upon who that person is.
+
+61
+00:02:20,000 --> 00:02:25,000
+What if somebody is asking for my children's name,
+
+62
+00:02:25,000 --> 00:02:27,000
+my wife name, my family name, my Facebook password?
+
+63
+00:02:27,000 --> 00:02:30,000
+No, I'm not going to share those things,
+
+64
+00:02:30,000 --> 00:02:32,000
+it's because there's something called privacy, right?
+
+65
+00:02:32,000 --> 00:02:34,000
+And yeah, I know a lot of people don't believe in privacy,
+
+66
+00:02:34,000 --> 00:02:36,000
+but of course no one should be able
+
+67
+00:02:36,000 --> 00:02:38,000
+to get your data directly, right?
+
+68
+00:02:38,000 --> 00:02:40,000
+It's not like your data is available
+
+69
+00:02:40,000 --> 00:02:41,000
+for the entire world to see.
+
+70
+00:02:41,000 --> 00:02:43,000
+It's there, it's closed.
+
+71
+00:02:43,000 --> 00:02:44,000
+No one can see the data.
+
+72
+00:02:44,000 --> 00:02:45,000
+Of course they can see my Facebook profile,
+
+73
+00:02:45,000 --> 00:02:48,000
+but no one can see the data inside your brain.
+
+74
+00:02:48,000 --> 00:02:50,000
+That's important.
+
+75
+00:02:50,000 --> 00:02:52,000
+If they want to know your data, they have to ask
+
+76
+00:02:52,000 --> 00:02:56,000
+and you can decide do you want to share or not?
+
+77
+00:02:56,000 --> 00:02:59,000
+In the same way, let's say we have this Human class
+
+78
+00:02:59,000 --> 00:03:01,000
+and in this Human class we have a variable called "age"
+
+79
+00:03:01,000 --> 00:03:03,000
+and we have a string which is "name",
+
+80
+00:03:03,000 --> 00:03:04,000
+that's it, just two variables.
+
+81
+00:03:04,000 --> 00:03:08,000
+And now if I want to access those data, of course I have
+
+82
+00:03:08,000 --> 00:03:10,000
+to create object of Human here.
+
+83
+00:03:10,000 --> 00:03:13,000
+And let's say this is the Human object, new Human.
+
+84
+00:03:13,000 --> 00:03:16,000
+And once you got this object, with this object,
+
+85
+00:03:16,000 --> 00:03:17,000
+you can fetch data, right?
+
+86
+00:03:17,000 --> 00:03:19,000
+Of course you can set the date values as well.
+
+87
+00:03:19,000 --> 00:03:21,000
+And for this particular object,
+
+88
+00:03:21,000 --> 00:03:24,000
+I can say obj.age is, let's say 11.
+
+89
+00:03:24,000 --> 00:03:29,000
+And obj.name is, let's say Navin.
+
+90
+00:03:29,000 --> 00:03:30,000
+I know that's not my age,
+
+91
+00:03:30,000 --> 00:03:33,000
+but at this point it's okay, so we got these values
+
+92
+00:03:33,000 --> 00:03:35,000
+and we got this object created here.
+
+93
+00:03:35,000 --> 00:03:40,000
+Now what I wanna do is, what if someone ask me, "Hey Human,"
+
+94
+00:03:40,000 --> 00:03:42,000
+or maybe someone is trying to directly trying
+
+95
+00:03:42,000 --> 00:03:43,000
+to fetch the data.
+
+96
+00:03:43,000 --> 00:03:47,000
+Example, if I say S out and if I try to say obj name.
+
+97
+00:03:47,000 --> 00:03:51,000
+Now what we are doing is just by using the object,
+
+98
+00:03:51,000 --> 00:03:53,000
+anyone can fetch data, okay?
+
+99
+00:03:53,000 --> 00:03:57,000
+And this will work, okay? It'll not give any issue.
+
+100
+00:03:57,000 --> 00:03:59,000
+So I will say compile and run.
+
+101
+00:03:59,000 --> 00:04:01,000
+You can see we are able to fetch data
+
+102
+00:04:01,000 --> 00:04:04,000
+and syntactically there's no issue.
+
+103
+00:04:04,000 --> 00:04:06,000
+But then if you really think that we have
+
+104
+00:04:06,000 --> 00:04:08,000
+to implement software for the physical world
+
+105
+00:04:08,000 --> 00:04:11,000
+or the real world, it should match with the real world.
+
+106
+00:04:11,000 --> 00:04:13,000
+Not all data are directly accessible
+
+107
+00:04:13,000 --> 00:04:15,000
+and we want to control it.
+
+108
+00:04:15,000 --> 00:04:16,000
+So one way to do that is
+
+109
+00:04:16,000 --> 00:04:19,000
+what you can do is you can make your variables private.
+
+110
+00:04:19,000 --> 00:04:21,000
+Now what do you mean by this private keyword?
+
+111
+00:04:21,000 --> 00:04:23,000
+Of course we'll have a detailed discussion later.
+
+112
+00:04:23,000 --> 00:04:25,000
+At this point, private simply means,
+
+113
+00:04:25,000 --> 00:04:28,000
+this particular variable, which is age,
+
+114
+00:04:28,000 --> 00:04:31,000
+is accessible only in the same class.
+
+115
+00:04:31,000 --> 00:04:32,000
+Let me repeat:
+
+116
+00:04:32,000 --> 00:04:37,000
+This age variable is accessible in the same class.
+
+117
+00:04:37,000 --> 00:04:39,000
+The moment you make it private, it's private.
+
+118
+00:04:39,000 --> 00:04:41,000
+No one from the outside world can use it.
+
+119
+00:04:41,000 --> 00:04:44,000
+Of course I can use my data because that's private to me,
+
+120
+00:04:44,000 --> 00:04:46,000
+but you can't access my data.
+
+121
+00:04:46,000 --> 00:04:49,000
+Because that's private to me, right?
+
+122
+00:04:49,000 --> 00:04:51,000
+The same thing can be done for the variable here.
+
+123
+00:04:51,000 --> 00:04:54,000
+And if you observe the moment I do that,
+
+124
+00:04:54,000 --> 00:04:56,000
+we got an error here.
+
+125
+00:04:56,000 --> 00:04:58,000
+I mean of course vs code helps you that.
+
+126
+00:04:58,000 --> 00:05:02,000
+VS code says, "Hey, this variable age is not visible."
+
+127
+00:05:02,000 --> 00:05:05,000
+You know why it's not visible? Because it's private!
+
+128
+00:05:05,000 --> 00:05:09,000
+Now going forward, this is what you have to do.
+
+129
+00:05:09,000 --> 00:05:12,000
+Every time you create a instance variable, let me repeat.
+
+130
+00:05:12,000 --> 00:05:17,000
+Every time you create a instance variable, make it private.
+
+131
+00:05:18,000 --> 00:05:20,000
+No one from the outside world should be able to use it.
+
+132
+00:05:20,000 --> 00:05:23,000
+Now you will say, "Hey, doing that,
+
+133
+00:05:23,000 --> 00:05:26,000
+we are actually breaking all the purpose
+
+134
+00:05:26,000 --> 00:05:27,000
+of building a software," right?
+
+135
+00:05:27,000 --> 00:05:29,000
+If no one is able to access this data,
+
+136
+00:05:29,000 --> 00:05:31,000
+then why we are even creating these variables?
+
+137
+00:05:31,000 --> 00:05:32,000
+That's right.
+
+138
+00:05:32,000 --> 00:05:34,000
+The reason why we are creating this variable
+
+139
+00:05:34,000 --> 00:05:35,000
+is because we can store values
+
+140
+00:05:35,000 --> 00:05:37,000
+and someone should be able to access them.
+
+141
+00:05:37,000 --> 00:05:41,000
+They should be able to access them but not directly.
+
+142
+00:05:41,000 --> 00:05:44,000
+So there should be some indirect way.
+
+143
+00:05:44,000 --> 00:05:45,000
+Yeah, we have indirect way.
+
+144
+00:05:45,000 --> 00:05:47,000
+So the way they should be able to access this data is
+
+145
+00:05:47,000 --> 00:05:49,000
+with the help of methods.
+
+146
+00:05:49,000 --> 00:05:52,000
+Example, let's say if you want to know my name, you have
+
+147
+00:05:52,000 --> 00:05:53,000
+to ask for it
+
+148
+00:05:53,000 --> 00:05:57,000
+and I will decide should I share that data with you or not?
+
+149
+00:05:57,000 --> 00:05:58,000
+So if you say, "Hey, what's your name?"
+
+150
+00:05:58,000 --> 00:06:01,000
+I will say, okay, I will ask my brain what's my name
+
+151
+00:06:01,000 --> 00:06:03,000
+because most of the time I don't remember my own name.
+
+152
+00:06:03,000 --> 00:06:05,000
+So I will say, hey, what's my name?
+
+153
+00:06:05,000 --> 00:06:07,000
+My brain will say, "Okay, your name is Navin."
+
+154
+00:06:07,000 --> 00:06:09,000
+And then from my methods, which is my mouth
+
+155
+00:06:09,000 --> 00:06:13,000
+or by using my handwriting or by typing somewhere,
+
+156
+00:06:13,000 --> 00:06:16,000
+there's a way I have to share that data with you, right?
+
+157
+00:06:16,000 --> 00:06:20,000
+I have some methods, behavior, I can talk,
+
+158
+00:06:20,000 --> 00:06:21,000
+I can write, I can type.
+
+159
+00:06:21,000 --> 00:06:24,000
+Now using those behavior, I can share the information, okay?
+
+160
+00:06:24,000 --> 00:06:26,000
+Not like anyone can just come to me,
+
+161
+00:06:26,000 --> 00:06:29,000
+they will break my head and say, "Okay, I got the data."
+
+162
+00:06:29,000 --> 00:06:31,000
+No, that's not how it should work.
+
+163
+00:06:31,000 --> 00:06:34,000
+So how do I restrict it?
+
+164
+00:06:34,000 --> 00:06:35,000
+So what we can do is we can make it private.
+
+165
+00:06:35,000 --> 00:06:37,000
+We are restricting it.
+
+166
+00:06:37,000 --> 00:06:40,000
+The only way to access them is with the help of methods.
+
+167
+00:06:40,000 --> 00:06:42,000
+So what I can do is temporary,
+
+168
+00:06:42,000 --> 00:06:44,000
+I will just come in these two sections
+
+169
+00:06:44,000 --> 00:06:48,000
+and I will assign the value here itself and we can do that.
+
+170
+00:06:48,000 --> 00:06:49,000
+I will say name is Navin,
+
+171
+00:06:49,000 --> 00:06:53,000
+and then here coming back to public, I will say public,
+
+172
+00:06:53,000 --> 00:06:54,000
+I want to get data.
+
+173
+00:06:54,000 --> 00:06:56,000
+I want to say, "Hey, get age," okay?
+
+174
+00:06:56,000 --> 00:06:59,000
+And of course you can use any method name, doesn't matter.
+
+175
+00:06:59,000 --> 00:07:03,000
+But let's say get age and this will return a integer value.
+
+176
+00:07:03,000 --> 00:07:06,000
+So I will say int here, and this will return.
+
+177
+00:07:06,000 --> 00:07:08,000
+So this will basically return the age.
+
+178
+00:07:08,000 --> 00:07:11,000
+Another question is, can I access age here?
+
+179
+00:07:11,000 --> 00:07:13,000
+And the answer is yes you can.
+
+180
+00:07:13,000 --> 00:07:16,000
+You can access the age variable inside a method
+
+181
+00:07:16,000 --> 00:07:17,000
+of a same class.
+
+182
+00:07:17,000 --> 00:07:19,000
+That's right.
+
+183
+00:07:19,000 --> 00:07:22,000
+This getAge is defined in the same class,
+
+184
+00:07:22,000 --> 00:07:24,000
+that's why you are able to access that.
+
+185
+00:07:24,000 --> 00:07:26,000
+And if you see age here or name here,
+
+186
+00:07:26,000 --> 00:07:29,000
+so we are trying to get the data of another class,
+
+187
+00:07:29,000 --> 00:07:33,000
+demo and Human, they are two different classes.
+
+188
+00:07:33,000 --> 00:07:34,000
+Okay, makes sense now.
+
+189
+00:07:34,000 --> 00:07:36,000
+Now we can also do it for the name.
+
+190
+00:07:36,000 --> 00:07:39,000
+So for the name I will say public string getName
+
+191
+00:07:40,000 --> 00:07:44,000
+and this will basically return a name.
+
+192
+00:07:44,000 --> 00:07:48,000
+Okay? So we got two methods, get age and get name.
+
+193
+00:07:48,000 --> 00:07:50,000
+And then we are returning the age and name.
+
+194
+00:07:50,000 --> 00:07:54,000
+Now if someone wants to fetch it, I can simply say,
+
+195
+00:07:54,000 --> 00:07:56,000
+"Hey, don't call name, that will not work."
+
+196
+00:07:56,000 --> 00:07:58,000
+Because name is a variable, this is private.
+
+197
+00:07:58,000 --> 00:08:02,000
+You can access the methods, you can say obj.getName
+
+198
+00:08:02,000 --> 00:08:04,000
+That's how you can fetch a value.
+
+199
+00:08:04,000 --> 00:08:06,000
+Of course you can also fetch the age.
+
+200
+00:08:06,000 --> 00:08:09,000
+What I can do is I can just say, plus I can give a colon
+
+201
+00:08:09,000 --> 00:08:12,000
+in between and I can say obj.getAge
+
+202
+00:08:12,000 --> 00:08:13,000
+Okay?
+
+203
+00:08:13,000 --> 00:08:17,000
+Now I think we should be able to access it.
+
+204
+00:08:17,000 --> 00:08:20,000
+Let's try and compile, run.
+
+205
+00:08:20,000 --> 00:08:21,000
+Oh it's working. Can you see that?
+
+206
+00:08:21,000 --> 00:08:23,000
+We got Navin and 11.
+
+207
+00:08:23,000 --> 00:08:27,000
+So the point remember is every time you create a variable
+
+208
+00:08:27,000 --> 00:08:30,000
+which is private, we are making sure that it is restricted.
+
+209
+00:08:30,000 --> 00:08:33,000
+No one from the outside world should be able to use it.
+
+210
+00:08:33,000 --> 00:08:36,000
+So this age variable, this name variable will be used
+
+211
+00:08:36,000 --> 00:08:38,000
+by their own methods.
+
+212
+00:08:38,000 --> 00:08:40,000
+That actually makes some sense.
+
+213
+00:08:40,000 --> 00:08:43,000
+But there's one little problem here.
+
+214
+00:08:43,000 --> 00:08:44,000
+What if I want to assign the value?
+
+215
+00:08:44,000 --> 00:08:48,000
+What if I don't specify the value here? Cut and cut.
+
+216
+00:08:48,000 --> 00:08:49,000
+Let's say we have the variables,
+
+217
+00:08:49,000 --> 00:08:51,000
+but I don't assign the value.
+
+218
+00:08:51,000 --> 00:08:53,000
+Now of course, if you don't assign the value,
+
+219
+00:08:53,000 --> 00:08:56,000
+default value will be zero and a null string.
+
+220
+00:08:56,000 --> 00:08:58,000
+But how do I set the value?
+
+221
+00:08:58,000 --> 00:09:02,000
+Now for getting the data we have said get,
+
+222
+00:09:02,000 --> 00:09:04,000
+for setting data, can we say set?
+
+223
+00:09:04,000 --> 00:09:05,000
+Let's try.
+
+224
+00:09:05,000 --> 00:09:07,000
+So here for age, I will say public.
+
+225
+00:09:07,000 --> 00:09:08,000
+Now when you are setting the value,
+
+226
+00:09:08,000 --> 00:09:10,000
+you're not getting in return something, right?
+
+227
+00:09:10,000 --> 00:09:14,000
+So you will say void and you will say setAge. Okay?
+
+228
+00:09:14,000 --> 00:09:16,000
+Now it's just that when you are setting the age, you have
+
+229
+00:09:16,000 --> 00:09:19,000
+to ask, "Hey, what is a value?"
+
+230
+00:09:19,000 --> 00:09:22,000
+So maybe you can also accept a value here,
+
+231
+00:09:22,000 --> 00:09:24,000
+maybe I can say A right?
+
+232
+00:09:24,000 --> 00:09:29,000
+And then here I can say age is equal to A.
+
+233
+00:09:29,000 --> 00:09:30,000
+Now what I mean by that is
+
+234
+00:09:30,000 --> 00:09:33,000
+of course you have a method which is accepting a value,
+
+235
+00:09:33,000 --> 00:09:35,000
+assigning that to age, but how it'll work?
+
+236
+00:09:35,000 --> 00:09:37,000
+So let's come back here, which the portion
+
+237
+00:09:37,000 --> 00:09:38,000
+which we have commented,
+
+238
+00:09:38,000 --> 00:09:39,000
+I want to set the age, right?
+
+239
+00:09:39,000 --> 00:09:41,000
+So instead of setting the age to the variable,
+
+240
+00:09:41,000 --> 00:09:44,000
+I can say obj.setAge
+
+241
+00:09:44,000 --> 00:09:46,000
+We are using a method now, not the variable.
+
+242
+00:09:46,000 --> 00:09:50,000
+And in this particular bracket you can pass the argument.
+
+243
+00:09:50,000 --> 00:09:52,000
+And let's say the age is 30.
+
+244
+00:09:52,000 --> 00:09:54,000
+So now we are passing the value.
+
+245
+00:09:54,000 --> 00:09:57,000
+Now this value will be assigned to this A
+
+246
+00:09:57,000 --> 00:10:00,000
+and from A, this will be assigned to age.
+
+247
+00:10:00,000 --> 00:10:02,000
+Can we do the same thing for string?
+
+248
+00:10:02,000 --> 00:10:06,000
+Let's try, I'll say public void setName
+
+249
+00:10:06,000 --> 00:10:09,000
+And of course we have to also accept the name.
+
+250
+00:10:09,000 --> 00:10:11,000
+But what's the format of name?
+
+251
+00:10:11,000 --> 00:10:14,000
+String name I will say N this time.
+
+252
+00:10:14,000 --> 00:10:18,000
+And here I can say name is equal to N.
+
+253
+00:10:18,000 --> 00:10:21,000
+So whatever value you pass, will be assigned to this n
+
+254
+00:10:21,000 --> 00:10:24,000
+and from N it'll be assigned to name.
+
+255
+00:10:24,000 --> 00:10:26,000
+Now the same thing need to be changed here.
+
+256
+00:10:26,000 --> 00:10:28,000
+So I will just cut this part
+
+257
+00:10:28,000 --> 00:10:29,000
+and I will say cut this part as well.
+
+258
+00:10:29,000 --> 00:10:31,000
+I will say set name.
+
+259
+00:10:31,000 --> 00:10:34,000
+And in the double codes I will pass the name.
+
+260
+00:10:34,000 --> 00:10:36,000
+And the name here is Navin.
+
+261
+00:10:36,000 --> 00:10:38,000
+Or maybe I'll use a different name
+
+262
+00:10:38,000 --> 00:10:39,000
+this time I will say Reddy.
+
+263
+00:10:39,000 --> 00:10:40,000
+Okay?
+
+264
+00:10:40,000 --> 00:10:43,000
+And now I will just come back here, clear the screen,
+
+265
+00:10:43,000 --> 00:10:45,000
+compile, run.
+
+266
+00:10:45,000 --> 00:10:48,000
+Now you see that we got Reddy and 30.
+
+267
+00:10:48,000 --> 00:10:50,000
+So what we are doing is we are assigning the value
+
+268
+00:10:50,000 --> 00:10:52,000
+with the help of methods here
+
+269
+00:10:52,000 --> 00:10:56,000
+and we are getting the value with the help of methods here.
+
+270
+00:10:56,000 --> 00:10:58,000
+So that's how we can access this data.
+
+271
+00:10:58,000 --> 00:11:02,000
+Now what we are doing is we are making your variable private
+
+272
+00:11:02,000 --> 00:11:04,000
+and then the only way to access them is
+
+273
+00:11:04,000 --> 00:11:05,000
+with the help of methods, right?
+
+274
+00:11:05,000 --> 00:11:08,000
+So basically we are binding our data with the methods.
+
+275
+00:11:08,000 --> 00:11:11,000
+The only way to access that data is with methods.
+
+276
+00:11:11,000 --> 00:11:13,000
+So no one from the outside world can use
+
+277
+00:11:13,000 --> 00:11:14,000
+your variables directly.
+
+278
+00:11:14,000 --> 00:11:17,000
+So somewhere we are encapsulating the data and methods
+
+279
+00:11:17,000 --> 00:11:19,000
+and that is Encapsulation.
+
+280
+00:11:19,000 --> 00:11:21,000
+Okay? Simple stuff, right?
+
+281
+00:11:21,000 --> 00:11:24,000
+So yeah, that's it from this video.
+
+282
+00:11:24,000 --> 00:11:26,000
+Let's try to understand this more.
+
+283
+00:11:26,000 --> 00:11:28,000
+What is this get and set methods?
+
+284
+00:11:28,000 --> 00:11:30,000
+Can we use different names
+
+285
+00:11:30,000 --> 00:11:32,000
+or only this name will work?
+
+286
+00:11:32,000 --> 00:11:34,000
+That we'll discuss in the next video.
+

02 - Core Java/044 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/045 Getters and setters_en.srt

@@ -0,0 +1,328 @@
+1
+00:00:00,000 --> 00:00:02,000
+(gentle music)
+
+2
+00:00:03,000 --> 00:00:06,000
+-: Let's try to understand what these methods are
+
+3
+00:00:06,000 --> 00:00:08,000
+or can we change the name?
+
+4
+00:00:08,000 --> 00:00:11,000
+So getAge, setAge makes sense,
+
+5
+00:00:11,000 --> 00:00:13,000
+but can we use some other names?
+
+6
+00:00:13,000 --> 00:00:14,000
+Actually, we can.
+
+7
+00:00:14,000 --> 00:00:16,000
+Instead of saying getAge, we can say abc,
+
+8
+00:00:16,000 --> 00:00:18,000
+and setAge, we can say xyz.
+
+9
+00:00:18,000 --> 00:00:20,000
+We can do that, okay? There's no harm in that.
+
+10
+00:00:20,000 --> 00:00:21,000
+The only thing is when you call these methods,
+
+11
+00:00:21,000 --> 00:00:23,000
+of course you have to change the name.
+
+12
+00:00:23,000 --> 00:00:25,000
+I will say this is xyz,
+
+13
+00:00:25,000 --> 00:00:28,000
+so when you set the value, you have to call xyz,
+
+14
+00:00:28,000 --> 00:00:31,000
+and then when you fetch the value, you have to say abc,
+
+15
+00:00:31,000 --> 00:00:32,000
+and it surely works.
+
+16
+00:00:32,000 --> 00:00:36,000
+If I try to compile this and run,
+
+17
+00:00:36,000 --> 00:00:37,000
+you can see it works.
+
+18
+00:00:37,000 --> 00:00:39,000
+Now, the problem with abc and xyz or any name
+
+19
+00:00:39,000 --> 00:00:44,000
+is your method name should define what is your intention.
+
+20
+00:00:44,000 --> 00:00:46,000
+Because most of the time it's not just about writing code,
+
+21
+00:00:46,000 --> 00:00:47,000
+it's also about reading code.
+
+22
+00:00:47,000 --> 00:00:49,000
+When you write a code once,
+
+23
+00:00:49,000 --> 00:00:51,000
+it will be read by multiple people
+
+24
+00:00:51,000 --> 00:00:53,000
+in the entire lifetime of a software.
+
+25
+00:00:53,000 --> 00:00:54,000
+Why not use proper words
+
+26
+00:00:54,000 --> 00:00:56,000
+which explains what that method is doing?
+
+27
+00:00:56,000 --> 00:00:58,000
+So instead of saying abc,
+
+28
+00:00:58,000 --> 00:01:00,000
+if I say getAge,
+
+29
+00:01:00,000 --> 00:01:01,000
+it is actually makes sense, right?
+
+30
+00:01:01,000 --> 00:01:04,000
+It is much more readable what you're doing there, right?
+
+31
+00:01:04,000 --> 00:01:06,000
+And as I mentioned before,
+
+32
+00:01:06,000 --> 00:01:08,000
+it is not a compulsion to use the same name.
+
+33
+00:01:08,000 --> 00:01:12,000
+But then as a Java developer, we have adopted this standard.
+
+34
+00:01:12,000 --> 00:01:15,000
+Whenever you want to get the value of a variable,
+
+35
+00:01:15,000 --> 00:01:17,000
+the method name would be get space,
+
+36
+00:01:17,000 --> 00:01:18,000
+the other variable name,
+
+37
+00:01:18,000 --> 00:01:19,000
+the variable name, which is age.
+
+38
+00:01:19,000 --> 00:01:20,000
+To set the value,
+
+39
+00:01:20,000 --> 00:01:22,000
+you will say set and you will use the variable name,
+
+40
+00:01:22,000 --> 00:01:24,000
+which is age, okay?
+
+41
+00:01:24,000 --> 00:01:25,000
+So, that's how we can use this.
+
+42
+00:01:25,000 --> 00:01:27,000
+So, this is called a getter.
+
+43
+00:01:27,000 --> 00:01:29,000
+So for the variable user, this is a getter.
+
+44
+00:01:29,000 --> 00:01:32,000
+And when you want to set the value,
+
+45
+00:01:32,000 --> 00:01:34,000
+so the method is called setter.
+
+46
+00:01:34,000 --> 00:01:38,000
+So, we can say that those are getters and setters.
+
+47
+00:01:38,000 --> 00:01:40,000
+In fact, the beauty is
+
+48
+00:01:40,000 --> 00:01:42,000
+if I delete the entire part,
+
+49
+00:01:42,000 --> 00:01:43,000
+okay, let me just do that.
+
+50
+00:01:43,000 --> 00:01:46,000
+I know we need to type that once again.
+
+51
+00:01:46,000 --> 00:01:47,000
+Actually, you don't.
+
+52
+00:01:47,000 --> 00:01:49,000
+Most of the IDEs have this amazing feature.
+
+53
+00:01:49,000 --> 00:01:52,000
+You can just right-click and there's a option of source.
+
+54
+00:01:52,000 --> 00:01:55,000
+In fact, it doesn't matter which IDE you're using,
+
+55
+00:01:55,000 --> 00:01:56,000
+you will see the option of source
+
+56
+00:01:56,000 --> 00:01:58,000
+or insert code, something like this.
+
+57
+00:01:58,000 --> 00:02:01,000
+So it will say Source Action, what do you want?
+
+58
+00:02:01,000 --> 00:02:03,000
+You want to get,
+
+59
+00:02:03,000 --> 00:02:07,000
+you have to say Generate Getters and Setters for me.
+
+60
+00:02:07,000 --> 00:02:08,000
+Click on that.
+
+61
+00:02:08,000 --> 00:02:09,000
+For both the variables,
+
+62
+00:02:09,000 --> 00:02:11,000
+and click on OK.
+
+63
+00:02:11,000 --> 00:02:14,000
+You can see it will generate the methods for you
+
+64
+00:02:14,000 --> 00:02:16,000
+and you see that variable names, it's same.
+
+65
+00:02:16,000 --> 00:02:21,000
+getAge, setAge, and then we got getName, setName, okay?
+
+66
+00:02:21,000 --> 00:02:23,000
+And those are called getters and setters.
+
+67
+00:02:23,000 --> 00:02:25,000
+And of course, there is no compulsion
+
+68
+00:02:25,000 --> 00:02:26,000
+to have both the methods.
+
+69
+00:02:26,000 --> 00:02:28,000
+You can only have getName.
+
+70
+00:02:28,000 --> 00:02:30,000
+You don't want to have setName, that's your choice.
+
+71
+00:02:30,000 --> 00:02:32,000
+There's no compulsion that there should be both.
+
+72
+00:02:32,000 --> 00:02:34,000
+It depends upon you how you want to implement it.
+
+73
+00:02:34,000 --> 00:02:38,000
+For this example, I want to assign value to age and name.
+
+74
+00:02:38,000 --> 00:02:39,000
+I want to get the values as well
+
+75
+00:02:39,000 --> 00:02:41,000
+and that's why I'm using this tool.
+
+76
+00:02:41,000 --> 00:02:42,000
+So only thing is for every variable,
+
+77
+00:02:42,000 --> 00:02:45,000
+you need two methods, getters and setters, okay?
+
+78
+00:02:45,000 --> 00:02:46,000
+So yeah, that's it.
+
+79
+00:02:46,000 --> 00:02:48,000
+But there's only one issue now.
+
+80
+00:02:48,000 --> 00:02:50,000
+If I use the code which is given by the IDE,
+
+81
+00:02:50,000 --> 00:02:53,000
+you can see this new keyword here, we got this.
+
+82
+00:02:53,000 --> 00:02:56,000
+What is this? So, let's talk about this in the next video.
+

02 - Core Java/045 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/046 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/046 This keyword_en.srt

@@ -0,0 +1,908 @@
+1
+00:00:00,000 --> 00:00:03,000
+(calm piano music)
+
+2
+00:00:03,000 --> 00:00:06,000
+-: In this video, let's talk about this
+
+3
+00:00:06,000 --> 00:00:07,000
+because in the previous video,
+
+4
+00:00:07,000 --> 00:00:08,000
+we were doing something
+
+5
+00:00:08,000 --> 00:00:10,000
+and then suddenly we got this keyword.
+
+6
+00:00:10,000 --> 00:00:13,000
+So it's important now to talk about this keyword here.
+
+7
+00:00:13,000 --> 00:00:15,000
+Now, what I will do is I will just remove this,
+
+8
+00:00:15,000 --> 00:00:19,000
+or I will just change this variable name back to A and N.
+
+9
+00:00:19,000 --> 00:00:24,000
+And of course, here, we have to say A and N, right?
+
+10
+00:00:24,000 --> 00:00:26,000
+And let me remove this keyword from here
+
+11
+00:00:26,000 --> 00:00:27,000
+just to see if this works.
+
+12
+00:00:27,000 --> 00:00:29,000
+Now, if I remove this keyword from there
+
+13
+00:00:29,000 --> 00:00:31,000
+and you find on this code compile, okay,
+
+14
+00:00:31,000 --> 00:00:34,000
+there is some problem with the variable names.
+
+15
+00:00:34,000 --> 00:00:36,000
+I think we are still calling X, Y, Z,
+
+16
+00:00:36,000 --> 00:00:37,000
+so it should be setAge.
+
+17
+00:00:38,000 --> 00:00:39,000
+And we are still calling A, B, C.
+
+18
+00:00:39,000 --> 00:00:42,000
+It should be getAge, the same thing
+
+19
+00:00:42,000 --> 00:00:44,000
+which we have done in the previous video.
+
+20
+00:00:44,000 --> 00:00:47,000
+Okay, so if I save this and if I go back and compile,
+
+21
+00:00:47,000 --> 00:00:51,000
+so compile, done, running, done,
+
+22
+00:00:51,000 --> 00:00:54,000
+so you can see we got the values right?
+
+23
+00:00:54,000 --> 00:00:56,000
+Now, the thing is when you talk about this variable like age
+
+24
+00:00:56,000 --> 00:00:58,000
+and when you are passing a here,
+
+25
+00:00:58,000 --> 00:01:00,000
+we are using two different variables right?
+
+26
+00:01:00,000 --> 00:01:04,000
+Now, the point to remember here is this a variable here
+
+27
+00:01:04,000 --> 00:01:05,000
+is a local variable.
+
+28
+00:01:05,000 --> 00:01:09,000
+This age variable here is a instance variable, right?
+
+29
+00:01:09,000 --> 00:01:11,000
+If you want to understand that with a diagram,
+
+30
+00:01:11,000 --> 00:01:13,000
+you can just go back here.
+
+31
+00:01:13,000 --> 00:01:15,000
+We have a stack memory, remember?
+
+32
+00:01:15,000 --> 00:01:17,000
+We have talked about stack and heap.
+
+33
+00:01:17,000 --> 00:01:19,000
+So we got a stack here and then we got heap here.
+
+34
+00:01:19,000 --> 00:01:22,000
+Now, the moment you create the human object,
+
+35
+00:01:22,000 --> 00:01:23,000
+we got this object here, Human.
+
+36
+00:01:23,000 --> 00:01:25,000
+So in this, we have a Human object
+
+37
+00:01:25,000 --> 00:01:29,000
+and of course, it will have some address, let's say, 101.
+
+38
+00:01:29,000 --> 00:01:32,000
+So we got obj and the address is 101.
+
+39
+00:01:32,000 --> 00:01:33,000
+That's the first object we got.
+
+40
+00:01:33,000 --> 00:01:37,000
+And there's a link here which we cannot ignore.
+
+41
+00:01:37,000 --> 00:01:39,000
+And then we have some more variables.
+
+42
+00:01:39,000 --> 00:01:41,000
+You can see if you execute.
+
+43
+00:01:41,000 --> 00:01:44,000
+And of course, this was my main stack.
+
+44
+00:01:45,000 --> 00:01:47,000
+Now, we are executing which method?
+
+45
+00:01:47,000 --> 00:01:52,000
+So if you say setAge, we are executing setAge method, right?
+
+46
+00:01:52,000 --> 00:01:54,000
+Now, setAge will have its own stack here.
+
+47
+00:01:54,000 --> 00:01:56,000
+Let's say, we have a setAge stack here.
+
+48
+00:01:56,000 --> 00:01:57,000
+You know what?
+
+49
+00:01:57,000 --> 00:01:59,000
+I just have to zoom it a bit
+
+50
+00:01:59,000 --> 00:02:01,000
+and here, let me create segments.
+
+51
+00:02:01,000 --> 00:02:04,000
+So we got multiple segments here
+
+52
+00:02:04,000 --> 00:02:05,000
+and of course, this will be linked
+
+53
+00:02:05,000 --> 00:02:08,000
+with this particular variable here.
+
+54
+00:02:08,000 --> 00:02:10,000
+And don't you think this box
+
+55
+00:02:10,000 --> 00:02:12,000
+which is address 101 is an object of Human?
+
+56
+00:02:12,000 --> 00:02:14,000
+So it will also have the instance variable.
+
+57
+00:02:14,000 --> 00:02:15,000
+How many instance variable we have.
+
+58
+00:02:15,000 --> 00:02:20,000
+We have age and name. So we got age and we got name here.
+
+59
+00:02:20,000 --> 00:02:23,000
+Now, if you look at the setAge, now setAge,
+
+60
+00:02:23,000 --> 00:02:27,000
+this particular stack is of setAge.
+
+61
+00:02:27,000 --> 00:02:28,000
+Every method will have its own stack.
+
+62
+00:02:28,000 --> 00:02:31,000
+And in this, we got a variable called a,
+
+63
+00:02:31,000 --> 00:02:34,000
+and the value for a which we are passing is study.
+
+64
+00:02:34,000 --> 00:02:36,000
+So we got 30 here, okay?
+
+65
+00:02:36,000 --> 00:02:40,000
+And then the same value 30, we are assigning to age.
+
+66
+00:02:40,000 --> 00:02:43,000
+That means we are changing this variable,
+
+67
+00:02:43,000 --> 00:02:45,000
+and we are assigning a value which is 30 there,
+
+68
+00:02:45,000 --> 00:02:47,000
+if that makes sense, okay?
+
+69
+00:02:47,000 --> 00:02:50,000
+So both the value for a and age is 30.
+
+70
+00:02:50,000 --> 00:02:52,000
+And that's why when you fetch data,
+
+71
+00:02:52,000 --> 00:02:56,000
+when you say getAge, it will return the value of age
+
+72
+00:02:56,000 --> 00:02:59,000
+in the object which is 30, in this case.
+
+73
+00:02:59,000 --> 00:03:00,000
+And that is perfectly working.
+
+74
+00:03:00,000 --> 00:03:03,000
+Now, the problem is what if I just make
+
+75
+00:03:03,000 --> 00:03:08,000
+this particular variable age as age, I mean, a as age?
+
+76
+00:03:08,000 --> 00:03:10,000
+Now, what I want is I want my local variable
+
+77
+00:03:10,000 --> 00:03:13,000
+and my instance variable both
+
+78
+00:03:13,000 --> 00:03:16,000
+to have the same variable name.
+
+79
+00:03:16,000 --> 00:03:19,000
+What do you mean by that is if I remove this a from here,
+
+80
+00:03:19,000 --> 00:03:22,000
+the variable name here will be age.
+
+81
+00:03:22,000 --> 00:03:25,000
+So both the variable name, the local variable
+
+82
+00:03:25,000 --> 00:03:28,000
+and the instance variable have the same name,
+
+83
+00:03:28,000 --> 00:03:30,000
+then it should work, right?
+
+84
+00:03:30,000 --> 00:03:31,000
+What we're trying to do is
+
+85
+00:03:31,000 --> 00:03:33,000
+the age variable will get 30 here.
+
+86
+00:03:33,000 --> 00:03:37,000
+So of course, in this stack, we got 30.
+
+87
+00:03:37,000 --> 00:03:40,000
+And if you see we are assigning age is equal to age.
+
+88
+00:03:40,000 --> 00:03:42,000
+So I'm expecting that this age will get the value
+
+89
+00:03:42,000 --> 00:03:45,000
+from this particular age. It should work, right?
+
+90
+00:03:45,000 --> 00:03:46,000
+Let's try.
+
+91
+00:03:46,000 --> 00:03:51,000
+If I go back to my code and compile and run,
+
+92
+00:03:51,000 --> 00:03:52,000
+oh, can you see that?
+
+93
+00:03:52,000 --> 00:03:54,000
+The value for age is still zero.
+
+94
+00:03:54,000 --> 00:03:56,000
+That means the assignment which we are assuming
+
+95
+00:03:56,000 --> 00:03:58,000
+that it will be 30, it is still zero.
+
+96
+00:03:58,000 --> 00:04:03,000
+Why? The reason is if we look at line number 11,
+
+97
+00:04:03,000 --> 00:04:07,000
+and if you see it, we are saying age is equal to age.
+
+98
+00:04:07,000 --> 00:04:10,000
+The problem is by default, now see,
+
+99
+00:04:10,000 --> 00:04:12,000
+this age can be local variable.
+
+100
+00:04:12,000 --> 00:04:14,000
+This age can be instance variable, right?
+
+101
+00:04:14,000 --> 00:04:17,000
+Because the names are same. So can we do this?
+
+102
+00:04:17,000 --> 00:04:21,000
+Can we say it is possible that
+
+103
+00:04:21,000 --> 00:04:24,000
+the age here is actually a local variable?
+
+104
+00:04:24,000 --> 00:04:26,000
+It is also possible that
+
+105
+00:04:26,000 --> 00:04:29,000
+the age is assigning value to itself.
+
+106
+00:04:29,000 --> 00:04:32,000
+Maybe this age is not even a instance variable.
+
+107
+00:04:32,000 --> 00:04:35,000
+That means this age is assigning value to itself
+
+108
+00:04:35,000 --> 00:04:39,000
+and this age here, which we have created,
+
+109
+00:04:39,000 --> 00:04:41,000
+it is still zero.
+
+110
+00:04:41,000 --> 00:04:42,000
+And that's why we are getting zero.
+
+111
+00:04:42,000 --> 00:04:44,000
+How do we solve this problem?
+
+112
+00:04:44,000 --> 00:04:46,000
+So somewhere we have to mention, hey, you know?
+
+113
+00:04:46,000 --> 00:04:48,000
+This particular age here, this is not a local variable.
+
+114
+00:04:48,000 --> 00:04:49,000
+This is an instance variable.
+
+115
+00:04:49,000 --> 00:04:52,000
+So remember this point, the preference will always give,
+
+116
+00:04:52,000 --> 00:04:54,000
+always be given to local variable.
+
+117
+00:04:54,000 --> 00:04:58,000
+So in case of confusion, it is always the local variable.
+
+118
+00:04:58,000 --> 00:04:59,000
+We have to mention by some way,
+
+119
+00:04:59,000 --> 00:05:01,000
+hey, this is not local variable.
+
+120
+00:05:01,000 --> 00:05:03,000
+That's an instance variable. How do you mention that?
+
+121
+00:05:03,000 --> 00:05:05,000
+So in order to say that's an instance variable,
+
+122
+00:05:05,000 --> 00:05:06,000
+can we do this?
+
+123
+00:05:06,000 --> 00:05:08,000
+Can we say Human?
+
+124
+00:05:08,000 --> 00:05:11,000
+Can we create object here itself, obj1 = new Human?
+
+125
+00:05:11,000 --> 00:05:14,000
+And then we can say obj1.age.
+
+126
+00:05:14,000 --> 00:05:16,000
+Now, what we are doing is we are saying
+
+127
+00:05:16,000 --> 00:05:19,000
+this age is a instance variable.
+
+128
+00:05:19,000 --> 00:05:20,000
+And you might be thinking,
+
+129
+00:05:20,000 --> 00:05:24,000
+hey, how can we use age with a object?
+
+130
+00:05:24,000 --> 00:05:24,000
+See, we can't do that
+
+131
+00:05:24,000 --> 00:05:27,000
+because we are in the same class, okay?
+
+132
+00:05:27,000 --> 00:05:28,000
+We were not able to do that here
+
+133
+00:05:28,000 --> 00:05:30,000
+because we were in different class.
+
+134
+00:05:30,000 --> 00:05:33,000
+But again, the problem is we are saying this age is instance
+
+135
+00:05:33,000 --> 00:05:35,000
+and this age is local, this should work.
+
+136
+00:05:35,000 --> 00:05:36,000
+Let's see if this is a problem
+
+137
+00:05:36,000 --> 00:05:38,000
+or we have solved the problem.
+
+138
+00:05:38,000 --> 00:05:42,000
+Let's run this. Oh, it is still zero. What is happening?
+
+139
+00:05:42,000 --> 00:05:44,000
+Let's try to understand more.
+
+140
+00:05:44,000 --> 00:05:46,000
+Now, when you execute this setAge method,
+
+141
+00:05:46,000 --> 00:05:49,000
+what we are doing is we are creating a new object.
+
+142
+00:05:49,000 --> 00:05:50,000
+Oh, that's the issue.
+
+143
+00:05:50,000 --> 00:05:54,000
+We are basically creating a new object.
+
+144
+00:05:54,000 --> 00:05:57,000
+Okay, how do we solve this problem?
+
+145
+00:05:57,000 --> 00:05:58,000
+We don't want to get new object
+
+146
+00:05:58,000 --> 00:06:00,000
+because the moment you create new object,
+
+147
+00:06:00,000 --> 00:06:02,000
+what will happen here is it will create a new object,
+
+148
+00:06:02,000 --> 00:06:04,000
+let's say 103.
+
+149
+00:06:04,000 --> 00:06:05,000
+And this will have,
+
+150
+00:06:05,000 --> 00:06:08,000
+this will also have age equal to name equal to,
+
+151
+00:06:08,000 --> 00:06:10,000
+and what value you're assigning here?
+
+152
+00:06:10,000 --> 00:06:11,000
+You're assigning value which is 30.
+
+153
+00:06:11,000 --> 00:06:16,000
+And then here in this setAge, you will create obj1
+
+154
+00:06:17,000 --> 00:06:20,000
+which will have the address 103 and there's a link here.
+
+155
+00:06:20,000 --> 00:06:22,000
+So the value which you are changing is
+
+156
+00:06:22,000 --> 00:06:25,000
+of this age, not this one.
+
+157
+00:06:25,000 --> 00:06:28,000
+We want to assign the value to this particular age.
+
+158
+00:06:28,000 --> 00:06:31,000
+That means creating a new object is not a good idea.
+
+159
+00:06:31,000 --> 00:06:34,000
+Okay, how do I clear this? Let's remove this.
+
+160
+00:06:34,000 --> 00:06:35,000
+In fact, you know? this is a problem.
+
+161
+00:06:35,000 --> 00:06:37,000
+This is creating a new object.
+
+162
+00:06:37,000 --> 00:06:39,000
+Okay, if I don't want to get a new object,
+
+163
+00:06:39,000 --> 00:06:42,000
+how do I access this obj?
+
+164
+00:06:42,000 --> 00:06:44,000
+Oh, I got an idea here.
+
+165
+00:06:44,000 --> 00:06:49,000
+What if with this 30, if I can pass the object itself,
+
+166
+00:06:49,000 --> 00:06:50,000
+can we, will it solve the problem?
+
+167
+00:06:50,000 --> 00:06:54,000
+With 30, if you can pass this particular object,
+
+168
+00:06:54,000 --> 00:06:58,000
+and we can accept the object here.
+
+169
+00:06:58,000 --> 00:07:02,000
+What type of object it is? It is human, Human obj.
+
+170
+00:07:02,000 --> 00:07:05,000
+And then here, we can simply assign the value.
+
+171
+00:07:05,000 --> 00:07:08,000
+So what I'm doing is if you observe correctly,
+
+172
+00:07:08,000 --> 00:07:10,000
+we are not creating a new object.
+
+173
+00:07:10,000 --> 00:07:14,000
+We are basically passing the reference of the old object.
+
+174
+00:07:14,000 --> 00:07:19,000
+So here, it will be not 103, it will be 101, okay?
+
+175
+00:07:21,000 --> 00:07:24,000
+So this obj1 here will get the address 101,
+
+176
+00:07:24,000 --> 00:07:27,000
+and we can simply say obj1.age.
+
+177
+00:07:27,000 --> 00:07:29,000
+And now, we are not referring to this address,
+
+178
+00:07:29,000 --> 00:07:31,000
+we are referring to this address.
+
+179
+00:07:31,000 --> 00:07:33,000
+So we can change the age value 30,
+
+180
+00:07:33,000 --> 00:07:35,000
+and let's see if this works.
+
+181
+00:07:35,000 --> 00:07:36,000
+I hope this will work.
+
+182
+00:07:36,000 --> 00:07:40,000
+Compile, sorry, compile, run.
+
+183
+00:07:40,000 --> 00:07:43,000
+Oh, it is working. It is working.
+
+184
+00:07:43,000 --> 00:07:44,000
+So basically, the important thing
+
+185
+00:07:44,000 --> 00:07:45,000
+is how do you differentiate
+
+186
+00:07:45,000 --> 00:07:48,000
+between instance variable and a local variable?
+
+187
+00:07:48,000 --> 00:07:51,000
+It's bypassing the object itself,
+
+188
+00:07:51,000 --> 00:07:54,000
+but there's one little problem here.
+
+189
+00:07:54,000 --> 00:07:59,000
+The problem is if you read this line, it says obj.setAge
+
+190
+00:07:59,000 --> 00:08:02,000
+and then you're passing the obj object as well.
+
+191
+00:08:02,000 --> 00:08:03,000
+Why we have to do this?
+
+192
+00:08:03,000 --> 00:08:08,000
+Why you have to mention obj two times. Now, Java knows this.
+
+193
+00:08:08,000 --> 00:08:10,000
+Java says, hey, you don't worry.
+
+194
+00:08:10,000 --> 00:08:11,000
+Why you have to pass the object two times?
+
+195
+00:08:11,000 --> 00:08:14,000
+I mean, you're calling the method by using the object.
+
+196
+00:08:14,000 --> 00:08:15,000
+You are also passing the object.
+
+197
+00:08:15,000 --> 00:08:18,000
+Don't do that. Don't pass the object.
+
+198
+00:08:18,000 --> 00:08:20,000
+By default, I will give you this obj.
+
+199
+00:08:20,000 --> 00:08:22,000
+You don't even have to accept this obj.
+
+200
+00:08:22,000 --> 00:08:25,000
+What if Java says, hey don't worry.
+
+201
+00:08:25,000 --> 00:08:27,000
+Don't create the object, don't pass the object.
+
+202
+00:08:27,000 --> 00:08:30,000
+I will give you the object and that object, my friend,
+
+203
+00:08:30,000 --> 00:08:33,000
+in fact, you know, when we had Human here,
+
+204
+00:08:33,000 --> 00:08:35,000
+we don't even need this Human line here.
+
+205
+00:08:35,000 --> 00:08:38,000
+We could have removed that and even obj would've worked.
+
+206
+00:08:38,000 --> 00:08:41,000
+So your Java says, hey, why do you even use this obj
+
+207
+00:08:41,000 --> 00:08:43,000
+when we can simply use this?
+
+208
+00:08:43,000 --> 00:08:48,000
+Now, this is a keyword which represents the current object.
+
+209
+00:08:48,000 --> 00:08:50,000
+Now, when I say current object, what it means?
+
+210
+00:08:50,000 --> 00:08:53,000
+The object which is calling the method.
+
+211
+00:08:53,000 --> 00:08:56,000
+SetAge is called OBJ, which is this object.
+
+212
+00:08:57,000 --> 00:09:00,000
+Here in this method, we can actually use that object
+
+213
+00:09:00,000 --> 00:09:02,000
+with the help of this keyword.
+
+214
+00:09:02,000 --> 00:09:04,000
+So this refers to the current object
+
+215
+00:09:04,000 --> 00:09:06,000
+who is calling the setAge.
+
+216
+00:09:06,000 --> 00:09:08,000
+I hope that makes sense.
+
+217
+00:09:08,000 --> 00:09:10,000
+So from this point, we are always
+
+218
+00:09:10,000 --> 00:09:13,000
+going to use this which represent the current object, okay?
+
+219
+00:09:13,000 --> 00:09:18,000
+So here as well, instead of using name or n,
+
+220
+00:09:18,000 --> 00:09:20,000
+I should have used name.
+
+221
+00:09:20,000 --> 00:09:21,000
+The only thing is we have to refer
+
+222
+00:09:21,000 --> 00:09:24,000
+the part, first name here is this.name,
+
+223
+00:09:24,000 --> 00:09:26,000
+which is the object itself.
+
+224
+00:09:26,000 --> 00:09:27,000
+The current object.
+
+225
+00:09:27,000 --> 00:09:30,000
+I hope this all this thing have made sense.
+
+226
+00:09:30,000 --> 00:09:32,000
+This is what this keyword is.
+
+227
+00:09:32,000 --> 00:09:34,000
+And yeah, that's it from this video.
+

02 - Core Java/047 Constructor_en.srt

@@ -0,0 +1,736 @@
+1
+00:00:00,000 --> 00:00:03,000
+(gentle piano music)
+
+2
+00:00:03,000 --> 00:00:06,000
+-: In this video, we'll talk about constructors.
+
+3
+00:00:06,000 --> 00:00:07,000
+Now what are constructors?
+
+4
+00:00:07,000 --> 00:00:09,000
+Now look at this example here, which is of human.
+
+5
+00:00:09,000 --> 00:00:10,000
+Now when you talk about human,
+
+6
+00:00:10,000 --> 00:00:11,000
+we have some variables, right?
+
+7
+00:00:11,000 --> 00:00:13,000
+Of course, when you talk about this two variables,
+
+8
+00:00:13,000 --> 00:00:15,000
+these are instance variable,
+
+9
+00:00:15,000 --> 00:00:18,000
+and then we have seen in the image as well.
+
+10
+00:00:18,000 --> 00:00:20,000
+Basically when you create an object example in this,
+
+11
+00:00:20,000 --> 00:00:23,000
+we are just creating one object,
+
+12
+00:00:23,000 --> 00:00:26,000
+and that object is getting created inside the heap memory.
+
+13
+00:00:26,000 --> 00:00:28,000
+You can see this is the object we got.
+
+14
+00:00:28,000 --> 00:00:29,000
+And of course with that object we have assigned
+
+15
+00:00:29,000 --> 00:00:31,000
+the value for the age,
+
+16
+00:00:31,000 --> 00:00:32,000
+we have assigned the value for the name as well,
+
+17
+00:00:32,000 --> 00:00:35,000
+which is ready. But I'm not return it here,
+
+18
+00:00:35,000 --> 00:00:38,000
+but we know that the object is created.
+
+19
+00:00:38,000 --> 00:00:41,000
+Now the thing is, when you create the object,
+
+20
+00:00:41,000 --> 00:00:43,000
+if you observe the line number 29,
+
+21
+00:00:43,000 --> 00:00:46,000
+on this line, when you create the object, what happens?
+
+22
+00:00:46,000 --> 00:00:48,000
+When you create the object in the heap memory,
+
+23
+00:00:48,000 --> 00:00:50,000
+it will just create a blank object.
+
+24
+00:00:50,000 --> 00:00:54,000
+Example. If I try to remove this, if I keep it empty,
+
+25
+00:00:54,000 --> 00:00:57,000
+it will create a object with a value.
+
+26
+00:00:57,000 --> 00:00:58,000
+So the value would be,
+
+27
+00:00:58,000 --> 00:01:01,000
+I mean it will have a variable which is age,
+
+28
+00:01:01,000 --> 00:01:02,000
+and the value will be zero,
+
+29
+00:01:02,000 --> 00:01:05,000
+and it will have a variable called a name,
+
+30
+00:01:05,000 --> 00:01:07,000
+and the value will be null, right?
+
+31
+00:01:07,000 --> 00:01:10,000
+I will just try to print those things.
+
+32
+00:01:10,000 --> 00:01:13,000
+What if I do is, I will just print the same statement
+
+33
+00:01:13,000 --> 00:01:15,000
+before assigning the value, right?
+
+34
+00:01:15,000 --> 00:01:18,000
+So I'm printing it here and I will command this section.
+
+35
+00:01:18,000 --> 00:01:19,000
+So that's how you command, right?
+
+36
+00:01:19,000 --> 00:01:21,000
+I don't want this time to be executed.
+
+37
+00:01:21,000 --> 00:01:24,000
+And now if I go back here and
+
+38
+00:01:24,000 --> 00:01:25,000
+compile
+
+39
+00:01:25,000 --> 00:01:27,000
+and run, you can see we got null.
+
+40
+00:01:27,000 --> 00:01:30,000
+Null basically is when you don't have the data assigned
+
+41
+00:01:30,000 --> 00:01:31,000
+to object type.
+
+42
+00:01:31,000 --> 00:01:34,000
+That's right. String is an object type.
+
+43
+00:01:34,000 --> 00:01:36,000
+We'll discuss about string later in detail.
+
+44
+00:01:36,000 --> 00:01:38,000
+As of now, just remember by default
+
+45
+00:01:38,000 --> 00:01:40,000
+the value for string is null,
+
+46
+00:01:40,000 --> 00:01:42,000
+and the default value for integer is zero.
+
+47
+00:01:42,000 --> 00:01:46,000
+Okay, that means if you don't assign this values,
+
+48
+00:01:46,000 --> 00:01:48,000
+there will be default values.
+
+49
+00:01:48,000 --> 00:01:49,000
+What I want here is,
+
+50
+00:01:49,000 --> 00:01:52,000
+of course there is a way you can assign the values later.
+
+51
+00:01:52,000 --> 00:01:54,000
+But what if I want to assign the value
+
+52
+00:01:54,000 --> 00:01:57,000
+when the object is created?
+
+53
+00:01:57,000 --> 00:01:59,000
+That's right, on this line itself,
+
+54
+00:01:59,000 --> 00:02:00,000
+I want to assign the value.
+
+55
+00:02:00,000 --> 00:02:02,000
+That means the moment I get the object,
+
+56
+00:02:02,000 --> 00:02:03,000
+I don't want to have a null value,
+
+57
+00:02:03,000 --> 00:02:05,000
+I want to have some default values.
+
+58
+00:02:05,000 --> 00:02:08,000
+Example, let's say by default every object created,
+
+59
+00:02:08,000 --> 00:02:09,000
+the name should be something else.
+
+60
+00:02:09,000 --> 00:02:12,000
+The name should be, let's say Babu or something else.
+
+61
+00:02:12,000 --> 00:02:14,000
+I'm not sure, but can we have a default name?
+
+62
+00:02:14,000 --> 00:02:16,000
+Can we have a default age?
+
+63
+00:02:16,000 --> 00:02:18,000
+So let's say for my application,
+
+64
+00:02:18,000 --> 00:02:20,000
+this application can be used only by those people
+
+65
+00:02:20,000 --> 00:02:23,000
+who are 12 and about.
+
+66
+00:02:23,000 --> 00:02:25,000
+So I can simply say, hey, the minimum age for this is 12.
+
+67
+00:02:25,000 --> 00:02:28,000
+So by default the value for the age should be 12.
+
+68
+00:02:28,000 --> 00:02:29,000
+Can we do that?
+
+69
+00:02:30,000 --> 00:02:32,000
+So how do we achieve that?
+
+70
+00:02:32,000 --> 00:02:34,000
+Of course, we can assign the values here,
+
+71
+00:02:34,000 --> 00:02:37,000
+or we can use something called a constructor.
+
+72
+00:02:37,000 --> 00:02:39,000
+Now how a constructor looks like,
+
+73
+00:02:39,000 --> 00:02:43,000
+so a constructor looks like a method itself.
+
+74
+00:02:43,000 --> 00:02:46,000
+Let me repeat. A constructor looks like a method itself.
+
+75
+00:02:46,000 --> 00:02:48,000
+That means a constructor will have a name,
+
+76
+00:02:48,000 --> 00:02:50,000
+a constructor will have the round brackets.
+
+77
+00:02:50,000 --> 00:02:53,000
+Example, if we talk about methods here we have a name
+
+78
+00:02:53,000 --> 00:02:56,000
+and we have a round bracket in the same way
+
+79
+00:02:56,000 --> 00:02:59,000
+for the constructor as well, we have to use that.
+
+80
+00:02:59,000 --> 00:03:01,000
+So what I will do is I will say public.
+
+81
+00:03:01,000 --> 00:03:03,000
+Now the only changes in the constructor,
+
+82
+00:03:03,000 --> 00:03:06,000
+you don't specify the written type.
+
+83
+00:03:06,000 --> 00:03:09,000
+Okay? So we can directly mention the constructor name here,
+
+84
+00:03:09,000 --> 00:03:12,000
+but what should be my constructor name?
+
+85
+00:03:12,000 --> 00:03:15,000
+Now there's a compulsion that your constructor name
+
+86
+00:03:15,000 --> 00:03:17,000
+should be same as your class name.
+
+87
+00:03:17,000 --> 00:03:19,000
+So what is my class name? It's human.
+
+88
+00:03:19,000 --> 00:03:20,000
+And then since it looks like a method,
+
+89
+00:03:20,000 --> 00:03:23,000
+we can give a round bracket and we can open and close
+
+90
+00:03:23,000 --> 00:03:24,000
+the curly brackets.
+
+91
+00:03:24,000 --> 00:03:27,000
+Now one thing I wanted to mention, you can see
+
+92
+00:03:27,000 --> 00:03:29,000
+with the curly packets are mentioned just I mean,
+
+93
+00:03:29,000 --> 00:03:31,000
+for the opening brackets are just
+
+94
+00:03:31,000 --> 00:03:32,000
+mentioned on the same line.
+
+95
+00:03:32,000 --> 00:03:35,000
+And here the curly brackets are mentioned on the new line,
+
+96
+00:03:35,000 --> 00:03:36,000
+both works.
+
+97
+00:03:36,000 --> 00:03:38,000
+Some people prefer to use on the same line,
+
+98
+00:03:38,000 --> 00:03:40,000
+some people prefer to use on next line.
+
+99
+00:03:40,000 --> 00:03:41,000
+So anything works.
+
+100
+00:03:41,000 --> 00:03:44,000
+Now in this constructor I can assign the values,
+
+101
+00:03:44,000 --> 00:03:46,000
+but at this point let's not assign the value,
+
+102
+00:03:46,000 --> 00:03:49,000
+I will just simply print the statement.
+
+103
+00:03:49,000 --> 00:03:54,000
+I will say is sout, and here I will print in constructor.
+
+104
+00:03:54,000 --> 00:03:56,000
+So you can see we are printing in constructor here.
+
+105
+00:03:56,000 --> 00:03:59,000
+So that's our constructor.
+
+106
+00:03:59,000 --> 00:04:00,000
+Okay, so let me repeat what is constructor?
+
+107
+00:04:00,000 --> 00:04:03,000
+So constructor is a special method, that's right,
+
+108
+00:04:03,000 --> 00:04:05,000
+because it looks like a method.
+
+109
+00:04:05,000 --> 00:04:06,000
+It has the same name as a class name.
+
+110
+00:04:06,000 --> 00:04:08,000
+So those are the rules you have to remember.
+
+111
+00:04:08,000 --> 00:04:11,000
+The constructor will have the same name as a class name.
+
+112
+00:04:11,000 --> 00:04:13,000
+A constructor never returns anything.
+
+113
+00:04:13,000 --> 00:04:15,000
+You don't have to mention int, float,
+
+114
+00:04:15,000 --> 00:04:16,000
+or string anything there.
+
+115
+00:04:16,000 --> 00:04:18,000
+So just specify the access, which is public,
+
+116
+00:04:18,000 --> 00:04:21,000
+and then mention the name, which is human.
+
+117
+00:04:21,000 --> 00:04:23,000
+And in this you can do whatever you want.
+
+118
+00:04:23,000 --> 00:04:26,000
+Okay, so I'm just printing in constructor.
+
+119
+00:04:26,000 --> 00:04:28,000
+So let me just try and compile.
+
+120
+00:04:28,000 --> 00:04:30,000
+So compilation done. There's no problem.
+
+121
+00:04:30,000 --> 00:04:34,000
+When I done this code, one thing to observe, nowhere,
+
+122
+00:04:34,000 --> 00:04:36,000
+see, when you talk about these methods like get age
+
+123
+00:04:36,000 --> 00:04:39,000
+or set age, all these methods we have called them, right?
+
+124
+00:04:39,000 --> 00:04:41,000
+So this is where you are calling them.
+
+125
+00:04:41,000 --> 00:04:44,000
+Constructor, you can see we are not calling it,
+
+126
+00:04:44,000 --> 00:04:48,000
+but still constructor will be called.
+
+127
+00:04:48,000 --> 00:04:50,000
+Okay, so even if we don't call it, it will be called.
+
+128
+00:04:50,000 --> 00:04:51,000
+Now when it will be called,
+
+129
+00:04:51,000 --> 00:04:53,000
+every time you create an object,
+
+130
+00:04:53,000 --> 00:04:55,000
+it will call the constructor.
+
+131
+00:04:55,000 --> 00:04:57,000
+So every time you create the object,
+
+132
+00:04:57,000 --> 00:04:59,000
+it will call the constructor.
+
+133
+00:04:59,000 --> 00:05:01,000
+Example, let's say if I create two objects,
+
+134
+00:05:01,000 --> 00:05:02,000
+I will just copy this line and paste it here.
+
+135
+00:05:02,000 --> 00:05:04,000
+Of course, I should have a different name
+
+136
+00:05:04,000 --> 00:05:05,000
+for the difference OBJ 1.
+
+137
+00:05:05,000 --> 00:05:08,000
+Now you can see we have two objects.
+
+138
+00:05:08,000 --> 00:05:09,000
+Now, when you say you have two objects,
+
+139
+00:05:09,000 --> 00:05:12,000
+and if I try to compile and run this,
+
+140
+00:05:12,000 --> 00:05:14,000
+you can see we got in constructor two times.
+
+141
+00:05:14,000 --> 00:05:17,000
+So every time you create a new object,
+
+142
+00:05:17,000 --> 00:05:19,000
+it will create a constructor,
+
+143
+00:05:19,000 --> 00:05:20,000
+or it will call the constructor.
+
+144
+00:05:20,000 --> 00:05:22,000
+Okay, if that makes sense.
+
+145
+00:05:22,000 --> 00:05:24,000
+What we can do is if we can remove this line
+
+146
+00:05:24,000 --> 00:05:28,000
+and I can assign the values, I can say age is equal to 12,
+
+147
+00:05:28,000 --> 00:05:32,000
+and name is equal to let's say by default, John,
+
+148
+00:05:32,000 --> 00:05:35,000
+of course you can have any name, but let's say John.
+
+149
+00:05:35,000 --> 00:05:40,000
+Now in this case I can see if this values are assigned.
+
+150
+00:05:40,000 --> 00:05:42,000
+What I can also do is I can just command this section.
+
+151
+00:05:42,000 --> 00:05:44,000
+Let's say I'm not assigning the values.
+
+152
+00:05:44,000 --> 00:05:46,000
+Let's see what are default values?
+
+153
+00:05:46,000 --> 00:05:48,000
+Compile, run, you can see we got John and 12.
+
+154
+00:05:48,000 --> 00:05:52,000
+So by default you assign this value.
+
+155
+00:05:52,000 --> 00:05:55,000
+Okay, so this is where constructors are helpful.
+
+156
+00:05:55,000 --> 00:05:56,000
+Now, you might be thinking,
+
+157
+00:05:56,000 --> 00:05:59,000
+hey, we can assign values here itself, right?
+
+158
+00:05:59,000 --> 00:06:02,000
+See, there's a idea, there's a standards which we follow,
+
+159
+00:06:02,000 --> 00:06:05,000
+whenever you want to perform any operation,
+
+160
+00:06:05,000 --> 00:06:07,000
+always do that in a method.
+
+161
+00:06:07,000 --> 00:06:11,000
+Don't openly do it in the statement like here,
+
+162
+00:06:11,000 --> 00:06:13,000
+if you want to perform some operation, like assignment,
+
+163
+00:06:13,000 --> 00:06:16,000
+or calculation, always doing the methods.
+
+164
+00:06:16,000 --> 00:06:19,000
+And constructor is like method, right?
+
+165
+00:06:19,000 --> 00:06:20,000
+So you can assign the values here.
+
+166
+00:06:20,000 --> 00:06:23,000
+There's no harm in terms of compilation.
+
+167
+00:06:23,000 --> 00:06:25,000
+You can assign the value here as well.
+
+168
+00:06:25,000 --> 00:06:27,000
+But we have to follow standards, right?
+
+169
+00:06:27,000 --> 00:06:29,000
+And also just try to think about something at once.
+
+170
+00:06:29,000 --> 00:06:32,000
+Let's say you are trying to connect with a database.
+
+171
+00:06:32,000 --> 00:06:35,000
+Now in that scenario, your application
+
+172
+00:06:35,000 --> 00:06:38,000
+is trying to connect with our database or the network.
+
+173
+00:06:38,000 --> 00:06:40,000
+You need that connection right?
+
+174
+00:06:40,000 --> 00:06:42,000
+Now where you will write the connection?
+
+175
+00:06:42,000 --> 00:06:45,000
+You can write the connections in the constructor.
+
+176
+00:06:45,000 --> 00:06:47,000
+And that's why this becomes very important.
+
+177
+00:06:47,000 --> 00:06:48,000
+Now, if you remember,
+
+178
+00:06:48,000 --> 00:06:50,000
+we have also talked about method overloading.
+
+179
+00:06:50,000 --> 00:06:53,000
+So when you have two methods with the same name
+
+180
+00:06:53,000 --> 00:06:54,000
+but different parameters,
+
+181
+00:06:54,000 --> 00:06:56,000
+those are called method overloading.
+
+182
+00:06:56,000 --> 00:07:00,000
+Now can we do that in constructor? That's tricky, right?
+
+183
+00:07:00,000 --> 00:07:02,000
+So let's discuss that in the next video.
+
+184
+00:07:02,000 --> 00:07:05,000
+How do we achieve constructor overloading.
+

02 - Core Java/047 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/048 Default vs Parameterized Constructor_en.srt

@@ -0,0 +1,520 @@
+1
+00:00:00,000 --> 00:00:03,000
+(gentle music)
+
+2
+00:00:03,000 --> 00:00:05,000
+-: Okay, so now we know what is constructor, right?
+
+3
+00:00:05,000 --> 00:00:09,000
+But what about this? I mean, can I pass the values here?
+
+4
+00:00:09,000 --> 00:00:12,000
+What if I don't want to assign values like 12 and John?
+
+5
+00:00:12,000 --> 00:00:14,000
+What if I want to customize it?
+
+6
+00:00:14,000 --> 00:00:17,000
+So, what I want is every time I create the object,
+
+7
+00:00:17,000 --> 00:00:20,000
+I should have an option of passing those values,
+
+8
+00:00:20,000 --> 00:00:22,000
+not 12 and John every time.
+
+9
+00:00:22,000 --> 00:00:23,000
+Can we do that?
+
+10
+00:00:23,000 --> 00:00:24,000
+Of course, you can assign the values later
+
+11
+00:00:24,000 --> 00:00:26,000
+with the help of site methods,
+
+12
+00:00:26,000 --> 00:00:29,000
+but what if I have an idea where, hey, you know,
+
+13
+00:00:29,000 --> 00:00:31,000
+I, okay, let's go with this object, as well,
+
+14
+00:00:31,000 --> 00:00:33,000
+the second object.
+
+15
+00:00:33,000 --> 00:00:35,000
+And in the second object, I want to pass the values.
+
+16
+00:00:35,000 --> 00:00:37,000
+The first object, I want it to be default.
+
+17
+00:00:37,000 --> 00:00:40,000
+The second object, I want the age to be, let's say 18.
+
+18
+00:00:40,000 --> 00:00:44,000
+And the name should be let's say Navin. Can we do that?
+
+19
+00:00:44,000 --> 00:00:46,000
+If you can see, this line is giving you error.
+
+20
+00:00:46,000 --> 00:00:49,000
+It says, hey, you know you don't have a constructor
+
+21
+00:00:49,000 --> 00:00:51,000
+which accepts two values,
+
+22
+00:00:51,000 --> 00:00:53,000
+so those two values of type integer and string,
+
+23
+00:00:53,000 --> 00:00:54,000
+you don't have it.
+
+24
+00:00:54,000 --> 00:00:56,000
+And if you go up, actually, you don't have it.
+
+25
+00:00:56,000 --> 00:00:59,000
+You don't have a constructor which takes two parameters.
+
+26
+00:00:59,000 --> 00:01:01,000
+Can we do that? Let's try.
+
+27
+00:01:01,000 --> 00:01:03,000
+So, I will say public Human,
+
+28
+00:01:03,000 --> 00:01:06,000
+and I want this Human to take two parameters.
+
+29
+00:01:06,000 --> 00:01:11,000
+So I will say int a, String name
+
+30
+00:01:11,000 --> 00:01:13,000
+and then here, I can just come back
+
+31
+00:01:13,000 --> 00:01:15,000
+and I can say age is equal to a.
+
+32
+00:01:15,000 --> 00:01:18,000
+So, not the default value which I want to assign here.
+
+33
+00:01:18,000 --> 00:01:21,000
+I want to assign the value which is sent by the main method.
+
+34
+00:01:21,000 --> 00:01:25,000
+So, if you can see, we are passing 18 and Navin here, right?
+
+35
+00:01:25,000 --> 00:01:27,000
+So I can just go back here.
+
+36
+00:01:27,000 --> 00:01:30,000
+And age is equal to a. Name is equal to n.
+
+37
+00:01:30,000 --> 00:01:33,000
+Now if you look at this particular constructor here,
+
+38
+00:01:33,000 --> 00:01:35,000
+it is taking some parameter.
+
+39
+00:01:35,000 --> 00:01:38,000
+So this constructor is called a parameterized constructor.
+
+40
+00:01:38,000 --> 00:01:40,000
+Oh, I should say this is n.
+
+41
+00:01:40,000 --> 00:01:43,000
+Now, what is the difference between normal constructor
+
+42
+00:01:43,000 --> 00:01:45,000
+and a parameterized constructor is, in fact,
+
+43
+00:01:45,000 --> 00:01:47,000
+this normal constructor is also called
+
+44
+00:01:47,000 --> 00:01:49,000
+a default constructor.
+
+45
+00:01:49,000 --> 00:01:51,000
+Now we'll discuss why this called default constructor.
+
+46
+00:01:51,000 --> 00:01:53,000
+So, this is called a default constructor.
+
+47
+00:01:53,000 --> 00:01:56,000
+This is called a parameterized constructor
+
+48
+00:01:56,000 --> 00:01:57,000
+because we have parameters there.
+
+49
+00:01:57,000 --> 00:02:00,000
+And whatever value you pass here will be assigned.
+
+50
+00:02:00,000 --> 00:02:01,000
+Now, you can use both syntax.
+
+51
+00:02:01,000 --> 00:02:03,000
+You can either create an object
+
+52
+00:02:03,000 --> 00:02:06,000
+by not specifying any parameter or arguments,
+
+53
+00:02:06,000 --> 00:02:11,000
+and you can create a object with the help of values,
+
+54
+00:02:11,000 --> 00:02:13,000
+which we are passing it here.
+
+55
+00:02:13,000 --> 00:02:16,000
+So, this is parameterized and this is default.
+
+56
+00:02:16,000 --> 00:02:17,000
+Now what I will do just to explain this,
+
+57
+00:02:17,000 --> 00:02:20,000
+is I will just copy the same line
+
+58
+00:02:20,000 --> 00:02:23,000
+and I will print the values for obj1 this time,
+
+59
+00:02:23,000 --> 00:02:24,000
+not for obj, obj1.
+
+60
+00:02:24,000 --> 00:02:26,000
+So basically, we are printing both
+
+61
+00:02:26,000 --> 00:02:27,000
+and let's see what the output is.
+
+62
+00:02:27,000 --> 00:02:29,000
+Compile, run.
+
+63
+00:02:29,000 --> 00:02:32,000
+You can see we got the first object, John : 12.
+
+64
+00:02:32,000 --> 00:02:33,000
+The second object is not John and 12.
+
+65
+00:02:33,000 --> 00:02:35,000
+It is Navin and 18
+
+66
+00:02:35,000 --> 00:02:36,000
+because you are passing those values.
+
+67
+00:02:36,000 --> 00:02:38,000
+Now what I will do this time and I will remove this part
+
+68
+00:02:38,000 --> 00:02:40,000
+just to explain you something.
+
+69
+00:02:40,000 --> 00:02:42,000
+See, when I mentioned that every time,
+
+70
+00:02:42,000 --> 00:02:44,000
+let me just commend this section, as well.
+
+71
+00:02:44,000 --> 00:02:47,000
+See, every time you create the object,
+
+72
+00:02:47,000 --> 00:02:50,000
+it will call the constructor, right?
+
+73
+00:02:50,000 --> 00:02:52,000
+But then if you see, I have removed the constructor.
+
+74
+00:02:52,000 --> 00:02:53,000
+Will this work?
+
+75
+00:02:53,000 --> 00:02:55,000
+And it was working before.
+
+76
+00:02:55,000 --> 00:02:56,000
+Remember when we started this example of Human,
+
+77
+00:02:56,000 --> 00:02:58,000
+we were not having any constructor.
+
+78
+00:02:58,000 --> 00:03:00,000
+It was still working.
+
+79
+00:03:00,000 --> 00:03:03,000
+At this point, your Java will say, hey, don't worry.
+
+80
+00:03:03,000 --> 00:03:05,000
+If you don't mention constructor there,
+
+81
+00:03:05,000 --> 00:03:07,000
+I will create a constructor for you.
+
+82
+00:03:07,000 --> 00:03:10,000
+And that's why we say that's a default constructor.
+
+83
+00:03:10,000 --> 00:03:13,000
+So behind the scene, you will get this constructor here,
+
+84
+00:03:13,000 --> 00:03:15,000
+which is public Human.
+
+85
+00:03:15,000 --> 00:03:18,000
+This is what you will get even if you don't mention, okay?
+
+86
+00:03:18,000 --> 00:03:20,000
+The only thing is it will be default.
+
+87
+00:03:20,000 --> 00:03:22,000
+It will be blank if you don't mention.
+
+88
+00:03:22,000 --> 00:03:23,000
+But if you want to do something, of course,
+
+89
+00:03:23,000 --> 00:03:25,000
+you have to mention that explicitly.
+
+90
+00:03:25,000 --> 00:03:27,000
+And we can use the same code
+
+91
+00:03:27,000 --> 00:03:31,000
+or I can actually ask my IDE to give me the code.
+
+92
+00:03:31,000 --> 00:03:34,000
+So, you can simply go to Source and Action
+
+93
+00:03:34,000 --> 00:03:37,000
+and you can say, hey, I want to create a constructor,
+
+94
+00:03:37,000 --> 00:03:38,000
+but which constructor?
+
+95
+00:03:38,000 --> 00:03:41,000
+So, I want a constructor which takes both these arguments.
+
+96
+00:03:41,000 --> 00:03:44,000
+And I also want a default constructor.
+
+97
+00:03:44,000 --> 00:03:46,000
+Source Action.
+
+98
+00:03:46,000 --> 00:03:48,000
+I want a constructor which is default.
+
+99
+00:03:48,000 --> 00:03:51,000
+You can see we got two constructors.
+
+100
+00:03:51,000 --> 00:03:52,000
+There's only one change.
+
+101
+00:03:52,000 --> 00:03:56,000
+The syntax which we have return was a and name,
+
+102
+00:03:56,000 --> 00:03:58,000
+and here if you can see, we have age and name.
+
+103
+00:03:58,000 --> 00:04:01,000
+And to make it work, we have to use this keyword.
+
+104
+00:04:01,000 --> 00:04:03,000
+I hope you remember this keyword video previously.
+
+105
+00:04:03,000 --> 00:04:06,000
+And that's how it works. It has the same way which works.
+
+106
+00:04:06,000 --> 00:04:08,000
+The only thing is we have to assign the values here.
+
+107
+00:04:08,000 --> 00:04:13,000
+I will say age is equal to 12 and the name is John.
+
+108
+00:04:13,000 --> 00:04:16,000
+So, that's how we can basically use a default constructor
+
+109
+00:04:16,000 --> 00:04:17,000
+and a parameterized constructor.
+
+110
+00:04:17,000 --> 00:04:19,000
+Of course, we can create some more constructor here.
+
+111
+00:04:19,000 --> 00:04:22,000
+What if you want to just specify the name,
+
+112
+00:04:22,000 --> 00:04:23,000
+not the role number?
+
+113
+00:04:23,000 --> 00:04:28,000
+So you can say, I want a constructor, Source Action,
+
+114
+00:04:29,000 --> 00:04:32,000
+and I want a constructor which takes only name.
+
+115
+00:04:32,000 --> 00:04:33,000
+So you can see we've got a constructor
+
+116
+00:04:33,000 --> 00:04:34,000
+which only takes a name.
+
+117
+00:04:34,000 --> 00:04:36,000
+Now what happens to this type of objects?
+
+118
+00:04:36,000 --> 00:04:38,000
+Example, if I create an object here,
+
+119
+00:04:38,000 --> 00:04:39,000
+let's say the second object,
+
+120
+00:04:39,000 --> 00:04:41,000
+and this time I'm not passing two values.
+
+121
+00:04:41,000 --> 00:04:43,000
+I'm just passing one value, which is name.
+
+122
+00:04:43,000 --> 00:04:47,000
+In this case, the age will be zero.
+
+123
+00:04:47,000 --> 00:04:49,000
+So what you can do is even if you're accepting name,
+
+124
+00:04:49,000 --> 00:04:52,000
+you can assign the age by year, so we can say 12.
+
+125
+00:04:52,000 --> 00:04:53,000
+You can say age because there's no confusion
+
+126
+00:04:53,000 --> 00:04:55,000
+or you can also say this.age
+
+127
+00:04:55,000 --> 00:04:57,000
+just to maintain the uniformity.
+
+128
+00:04:57,000 --> 00:05:00,000
+Okay, so that's how we use constructors,
+
+129
+00:05:00,000 --> 00:05:03,000
+default constructors, parameterized constructors,
+
+130
+00:05:03,000 --> 00:05:04,000
+and yeah, that's it.
+

02 - Core Java/048 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/049 Naming Convention_en.srt

@@ -0,0 +1,440 @@
+1
+00:00:00,000 --> 00:00:03,000
+(gentle music)
+
+2
+00:00:03,000 --> 00:00:06,000
+-: In this video, let's talk about the naming conventions.
+
+3
+00:00:06,000 --> 00:00:08,000
+Now, if you see the code which we are written till now,
+
+4
+00:00:08,000 --> 00:00:11,000
+somewhere, I was using capital letters,
+
+5
+00:00:11,000 --> 00:00:13,000
+I was using small letters.
+
+6
+00:00:13,000 --> 00:00:14,000
+When to use what?
+
+7
+00:00:14,000 --> 00:00:17,000
+And then what if you want to join two words?
+
+8
+00:00:17,000 --> 00:00:19,000
+How will you make it more readable?
+
+9
+00:00:19,000 --> 00:00:21,000
+Now that's where Java says it follows a naming convention
+
+10
+00:00:21,000 --> 00:00:22,000
+of camel casing.
+
+11
+00:00:22,000 --> 00:00:26,000
+So basically, it uses camel casing.
+
+12
+00:00:26,000 --> 00:00:27,000
+Now, what camel casing means,
+
+13
+00:00:27,000 --> 00:00:30,000
+or let's talk about in general how do we name our classes?
+
+14
+00:00:30,000 --> 00:00:32,000
+Now, whenever you create a class,
+
+15
+00:00:32,000 --> 00:00:34,000
+a class name should start with a capital letter.
+
+16
+00:00:34,000 --> 00:00:36,000
+So when you talk about class,
+
+17
+00:00:36,000 --> 00:00:37,000
+it should start with a capital letter.
+
+18
+00:00:37,000 --> 00:00:40,000
+Example, if you want to get a class called Calculator,
+
+19
+00:00:40,000 --> 00:00:41,000
+the C should be capital.
+
+20
+00:00:41,000 --> 00:00:44,000
+Now on the other hand, if you talk about variables
+
+21
+00:00:44,000 --> 00:00:48,000
+or methods, so for variable and methods,
+
+22
+00:00:48,000 --> 00:00:52,000
+what you will follow is you will start with a small letter.
+
+23
+00:00:52,000 --> 00:00:54,000
+Example, if your variable name can be marks,
+
+24
+00:00:54,000 --> 00:00:56,000
+a method name can be show.
+
+25
+00:00:56,000 --> 00:00:58,000
+So, it will always start with small.
+
+26
+00:00:58,000 --> 00:01:02,000
+Class, capital, variable, method, small.
+
+27
+00:01:02,000 --> 00:01:04,000
+In fact, we also have a concept of interfaces,
+
+28
+00:01:04,000 --> 00:01:05,000
+which we'll discuss later.
+
+29
+00:01:05,000 --> 00:01:08,000
+So if we talk about classes and interface,
+
+30
+00:01:08,000 --> 00:01:10,000
+we'll have to make it capital.
+
+31
+00:01:10,000 --> 00:01:12,000
+Let's say interface is Runable.
+
+32
+00:01:12,000 --> 00:01:14,000
+So basically, this is the convention which we follow.
+
+33
+00:01:14,000 --> 00:01:17,000
+Class, interface, we have capital letters,
+
+34
+00:01:17,000 --> 00:01:19,000
+variable, methods, we have small letters.
+
+35
+00:01:19,000 --> 00:01:21,000
+We also have a concept of constants,
+
+36
+00:01:21,000 --> 00:01:23,000
+which we have talked about.
+
+37
+00:01:23,000 --> 00:01:27,000
+So when you talk about constants, it will have a capital,
+
+38
+00:01:27,000 --> 00:01:28,000
+but all capital.
+
+39
+00:01:28,000 --> 00:01:30,000
+Example, if we talk about the value of PIE,
+
+40
+00:01:30,000 --> 00:01:34,000
+if we talk about a constant of BRAND,
+
+41
+00:01:34,000 --> 00:01:35,000
+so doesn't matter what your constant is.
+
+42
+00:01:35,000 --> 00:01:39,000
+So you can have all capital here. Now, why do we do this?
+
+43
+00:01:39,000 --> 00:01:41,000
+We do this just to see and understand
+
+44
+00:01:41,000 --> 00:01:43,000
+what could be the thing which you are doing.
+
+45
+00:01:43,000 --> 00:01:46,000
+Example, if you say, if you see this type of things,
+
+46
+00:01:46,000 --> 00:01:49,000
+you can guess, hey, it can be a class or interface.
+
+47
+00:01:49,000 --> 00:01:52,000
+If you look at this, you know this is a variable.
+
+48
+00:01:52,000 --> 00:01:54,000
+If you look at this, you know this is a method.
+
+49
+00:01:54,000 --> 00:01:57,000
+And when you look at this, you know these are constants.
+
+50
+00:01:57,000 --> 00:01:59,000
+It makes your code much more readable.
+
+51
+00:01:59,000 --> 00:02:00,000
+And that's important, right?
+
+52
+00:02:00,000 --> 00:02:03,000
+It's very easy to write a code which works.
+
+53
+00:02:03,000 --> 00:02:05,000
+It's difficult to write a code which anyone can read,
+
+54
+00:02:05,000 --> 00:02:08,000
+and that's why you should follow this convention.
+
+55
+00:02:08,000 --> 00:02:11,000
+So, this is how you use the main convention.
+
+56
+00:02:11,000 --> 00:02:14,000
+But what if you have a word which which has two letters?
+
+57
+00:02:14,000 --> 00:02:17,000
+Example, if you talk about, show my marks.
+
+58
+00:02:17,000 --> 00:02:21,000
+If I want to do this, so you have to say, showMyMarks,
+
+59
+00:02:21,000 --> 00:02:24,000
+because if you say showmymarks,
+
+60
+00:02:24,000 --> 00:02:27,000
+it is actually a bit difficult to read, right?
+
+61
+00:02:27,000 --> 00:02:30,000
+So what you can do is every time you combine words,
+
+62
+00:02:30,000 --> 00:02:31,000
+make sure that the first letter of the second word
+
+63
+00:02:31,000 --> 00:02:34,000
+or the first letter make it capital.
+
+64
+00:02:34,000 --> 00:02:37,000
+It makes it much more readable compared to small letters.
+
+65
+00:02:37,000 --> 00:02:39,000
+Now, this is what camel casing means.
+
+66
+00:02:39,000 --> 00:02:41,000
+You know we have camel, so it goes up and down.
+
+67
+00:02:41,000 --> 00:02:45,000
+So we have small letters, then we have in between,
+
+68
+00:02:45,000 --> 00:02:47,000
+we have capital, small, again, we have capital.
+
+69
+00:02:47,000 --> 00:02:49,000
+So this is camel casing.
+
+70
+00:02:49,000 --> 00:02:51,000
+Now, apart from this, there are different languages
+
+71
+00:02:51,000 --> 00:02:53,000
+which follow snake casing rule
+
+72
+00:02:53,000 --> 00:02:54,000
+where we use underscores.
+
+73
+00:02:54,000 --> 00:02:58,000
+Example, in some languages, they follow snake casing.
+
+74
+00:02:58,000 --> 00:02:59,000
+They use underscore.
+
+75
+00:02:59,000 --> 00:03:01,000
+And people who jump between different languages,
+
+76
+00:03:01,000 --> 00:03:04,000
+they get this tendency of using underscore.
+
+77
+00:03:04,000 --> 00:03:06,000
+So, again, Java will not give you any error,
+
+78
+00:03:06,000 --> 00:03:08,000
+but if you follow the Java pattern,
+
+79
+00:03:08,000 --> 00:03:10,000
+Java developers will not like this.
+
+80
+00:03:10,000 --> 00:03:12,000
+So, if you're writing a code where you have a Java team
+
+81
+00:03:12,000 --> 00:03:15,000
+or everyone who works on Java, try to follow camel casing
+
+82
+00:03:15,000 --> 00:03:18,000
+and, but again, it will not give you error.
+
+83
+00:03:18,000 --> 00:03:19,000
+It perfectly works.
+
+84
+00:03:19,000 --> 00:03:22,000
+Underscore works in the names, but that's what we follow.
+
+85
+00:03:22,000 --> 00:03:26,000
+We follow camel casing here, not snake casing, yeah?
+
+86
+00:03:26,000 --> 00:03:29,000
+If you have the class name, which is again,
+
+87
+00:03:29,000 --> 00:03:32,000
+I want to say MyData is a class,
+
+88
+00:03:32,000 --> 00:03:36,000
+so you can say M is capital because that's a class name.
+
+89
+00:03:36,000 --> 00:03:38,000
+Now I will give you, I will show you some names
+
+90
+00:03:38,000 --> 00:03:40,000
+and you have to guess what those are.
+
+91
+00:03:40,000 --> 00:03:44,000
+Example, if I say age, that's variable, right, okay?
+
+92
+00:03:44,000 --> 00:03:47,000
+What if I say DATA? What is this?
+
+93
+00:03:47,000 --> 00:03:51,000
+This is a constant because everything is capital, okay?
+
+94
+00:03:51,000 --> 00:03:54,000
+Yeah, in terms of constant, if you want to say my data,
+
+95
+00:03:54,000 --> 00:03:56,000
+which is a constant, you have to use MYDATA,
+
+96
+00:03:56,000 --> 00:03:58,000
+but again, everything is capital, right?
+
+97
+00:03:58,000 --> 00:03:59,000
+So at this point, you can use underscore
+
+98
+00:03:59,000 --> 00:04:02,000
+just to differentiate this, and again,
+
+99
+00:04:02,000 --> 00:04:03,000
+these are the good practices which I'm showing you.
+
+100
+00:04:03,000 --> 00:04:04,000
+How about this?
+
+101
+00:04:04,000 --> 00:04:08,000
+If I use something like Human, but I use a round bracket.
+
+102
+00:04:08,000 --> 00:04:10,000
+Any guess? Yeah, that's a constructor.
+
+103
+00:04:10,000 --> 00:04:11,000
+Why is a constructor?
+
+104
+00:04:11,000 --> 00:04:14,000
+Is because the first letter is capital.
+
+105
+00:04:14,000 --> 00:04:16,000
+That means it represents a class name.
+
+106
+00:04:16,000 --> 00:04:17,000
+And we also have a round bracket,
+
+107
+00:04:17,000 --> 00:04:20,000
+method like something, so that's a constructor.
+
+108
+00:04:20,000 --> 00:04:22,000
+So this is a naming convention which we follow
+
+109
+00:04:22,000 --> 00:04:25,000
+and try to use good names for your variables, your classes,
+
+110
+00:04:25,000 --> 00:04:29,000
+your methods, so that it will be easy for others to read.
+

02 - Core Java/049 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/050 Anonymous Object_en.srt

@@ -0,0 +1,508 @@
+1
+00:00:00,000 --> 00:00:03,000
+(gentle piano music)
+
+2
+00:00:03,000 --> 00:00:05,000
+-: Okay, so now we know how to create the object, right?
+
+3
+00:00:05,000 --> 00:00:06,000
+So we have a class.
+
+4
+00:00:06,000 --> 00:00:08,000
+Let's say we have a class A,
+
+5
+00:00:08,000 --> 00:00:10,000
+and then in this class A, we have a show method.
+
+6
+00:00:10,000 --> 00:00:11,000
+Now, how do we call show method?
+
+7
+00:00:11,000 --> 00:00:12,000
+That's very simple.
+
+8
+00:00:12,000 --> 00:00:14,000
+First you have to create the object of A,
+
+9
+00:00:14,000 --> 00:00:16,000
+and then you can call the show method.
+
+10
+00:00:16,000 --> 00:00:17,000
+Now what happens behind the scenes?
+
+11
+00:00:17,000 --> 00:00:21,000
+So of course you have your big JVM here,
+
+12
+00:00:21,000 --> 00:00:24,000
+and then in this you'll be having your stack memory
+
+13
+00:00:24,000 --> 00:00:26,000
+and then you'll be having your heap memory as well.
+
+14
+00:00:26,000 --> 00:00:29,000
+Now, in this heap memory, so if you look at line number 14,
+
+15
+00:00:29,000 --> 00:00:31,000
+it will create an object.
+
+16
+00:00:31,000 --> 00:00:33,000
+Let's say the address is 1 0 1,
+
+17
+00:00:33,000 --> 00:00:36,000
+and then in this you'll be having a variable or methods.
+
+18
+00:00:36,000 --> 00:00:37,000
+We don't have a variable as of now.
+
+19
+00:00:37,000 --> 00:00:39,000
+So let's say we have a method which is show.
+
+20
+00:00:39,000 --> 00:00:41,000
+So of course in order to call this show, we need objects.
+
+21
+00:00:41,000 --> 00:00:44,000
+So we have done that, and then we have OBJ here.
+
+22
+00:00:44,000 --> 00:00:48,000
+The address will be 1 0 1 and it will refer here.
+
+23
+00:00:48,000 --> 00:00:50,000
+And then every time you want to call show,
+
+24
+00:00:50,000 --> 00:00:54,000
+basically you have to say obj.show.
+
+25
+00:00:54,000 --> 00:00:56,000
+That's how it works, right? Okay.
+
+26
+00:00:56,000 --> 00:00:58,000
+Now just to clear the things,
+
+27
+00:00:58,000 --> 00:01:01,000
+this OBJ here is not called the object.
+
+28
+00:01:01,000 --> 00:01:04,000
+It is called a reference variable, right?
+
+29
+00:01:04,000 --> 00:01:07,000
+So this is your reference variable.
+
+30
+00:01:07,000 --> 00:01:08,000
+Why this called a reference variable?
+
+31
+00:01:08,000 --> 00:01:09,000
+Because it's referring to an object.
+
+32
+00:01:09,000 --> 00:01:10,000
+The object is here.
+
+33
+00:01:10,000 --> 00:01:13,000
+So this is your object, okay?
+
+34
+00:01:13,000 --> 00:01:15,000
+So the question is, if I want to create this object,
+
+35
+00:01:15,000 --> 00:01:18,000
+is this line compulsory or do we have a shortcut?
+
+36
+00:01:18,000 --> 00:01:19,000
+Now to understand this mode,
+
+37
+00:01:19,000 --> 00:01:21,000
+let's also use a concept of constructor.
+
+38
+00:01:21,000 --> 00:01:23,000
+So let's say we have a constructor here, which is A,
+
+39
+00:01:23,000 --> 00:01:26,000
+and then I'm just trying to print something here,
+
+40
+00:01:26,000 --> 00:01:28,000
+it says object created.
+
+41
+00:01:28,000 --> 00:01:30,000
+So of course we know every time you create the object,
+
+42
+00:01:30,000 --> 00:01:33,000
+it will call the constructor as well.
+
+43
+00:01:33,000 --> 00:01:33,000
+So it should print.
+
+44
+00:01:33,000 --> 00:01:36,000
+So if I compile and run this code,
+
+45
+00:01:36,000 --> 00:01:38,000
+you can see it says object created
+
+46
+00:01:38,000 --> 00:01:40,000
+and it is printing in a show.
+
+47
+00:01:40,000 --> 00:01:42,000
+Now, actually, if you look at this line here,
+
+48
+00:01:42,000 --> 00:01:44,000
+there are two steps, not one.
+
+49
+00:01:44,000 --> 00:01:46,000
+Example, so let's say if you create
+
+50
+00:01:46,000 --> 00:01:49,000
+a local variable called marks, okay?
+
+51
+00:01:49,000 --> 00:01:51,000
+And then you set the marks for it,
+
+52
+00:01:51,000 --> 00:01:52,000
+you set the value for it.
+
+53
+00:01:52,000 --> 00:01:54,000
+Let's say 99,
+
+54
+00:01:54,000 --> 00:01:56,000
+we hate, everyone hates this type of people, right?
+
+55
+00:01:56,000 --> 00:01:58,000
+Anyway, so we have this variable.
+
+56
+00:01:58,000 --> 00:02:00,000
+So what we are doing is we are first of all
+
+57
+00:02:00,000 --> 00:02:04,000
+declaring the variable and then we are as assigning a value.
+
+58
+00:02:04,000 --> 00:02:06,000
+The same thing can be done for this thing, right?
+
+59
+00:02:06,000 --> 00:02:08,000
+We can do it in two steps.
+
+60
+00:02:08,000 --> 00:02:09,000
+We can declare the object
+
+61
+00:02:09,000 --> 00:02:13,000
+and then we can say OBJ equal to new A.
+
+62
+00:02:13,000 --> 00:02:15,000
+Now this is called reference creation, right?
+
+63
+00:02:15,000 --> 00:02:17,000
+This is where you're creating a reference and then
+
+64
+00:02:17,000 --> 00:02:19,000
+this is where you are creating an object
+
+65
+00:02:19,000 --> 00:02:23,000
+and assigning the value to OBJ.
+
+66
+00:02:23,000 --> 00:02:26,000
+That means this is, I mean, when you say new A,
+
+67
+00:02:26,000 --> 00:02:29,000
+this is where you create the object.
+
+68
+00:02:29,000 --> 00:02:30,000
+Let me show that.
+
+69
+00:02:30,000 --> 00:02:35,000
+Let me remove everything from here and say new A,
+
+70
+00:02:35,000 --> 00:02:38,000
+this is object creation, not the entire line.
+
+71
+00:02:38,000 --> 00:02:41,000
+When you say new A constructor,
+
+72
+00:02:41,000 --> 00:02:43,000
+that is your object creation.
+
+73
+00:02:43,000 --> 00:02:45,000
+The moment you do that in your heap memory,
+
+74
+00:02:45,000 --> 00:02:48,000
+of course we don't have all this data now,
+
+75
+00:02:48,000 --> 00:02:50,000
+so ignore all this data, which is there,
+
+76
+00:02:50,000 --> 00:02:52,000
+let me just remove this. This is not there.
+
+77
+00:02:52,000 --> 00:02:53,000
+Imagine there's no object.
+
+78
+00:02:53,000 --> 00:02:55,000
+So this line will create an object,
+
+79
+00:02:55,000 --> 00:02:58,000
+doesn't matter what's the address. Let's say 5 0 1,
+
+80
+00:02:58,000 --> 00:03:01,000
+and it will have this show method, okay?
+
+81
+00:03:01,000 --> 00:03:04,000
+The only thing is we are not doing anything.
+
+82
+00:03:04,000 --> 00:03:06,000
+We are not creating any variable inside stack.
+
+83
+00:03:06,000 --> 00:03:10,000
+Example, when you say int marks, the moment you do that,
+
+84
+00:03:10,000 --> 00:03:13,000
+it will create a int variable called marks, here.
+
+85
+00:03:13,000 --> 00:03:15,000
+The value will be blank.
+
+86
+00:03:15,000 --> 00:03:17,000
+And whatever value you want to assign,
+
+87
+00:03:17,000 --> 00:03:18,000
+you can assign that here.
+
+88
+00:03:18,000 --> 00:03:20,000
+But if you can see, we are not doing anything here.
+
+89
+00:03:20,000 --> 00:03:22,000
+We are just creating a object,
+
+90
+00:03:22,000 --> 00:03:26,000
+that is created inside the heap memory, nothing in stack.
+
+91
+00:03:26,000 --> 00:03:29,000
+And if you don't trust me, let me just show you the proof.
+
+92
+00:03:29,000 --> 00:03:34,000
+If I compile this code and run, it says object created.
+
+93
+00:03:34,000 --> 00:03:36,000
+This is the object,
+
+94
+00:03:36,000 --> 00:03:40,000
+and this type of objects are called anonymous object.
+
+95
+00:03:40,000 --> 00:03:40,000
+You know why?
+
+96
+00:03:40,000 --> 00:03:43,000
+It's because this type of object don't have a name, right?
+
+97
+00:03:43,000 --> 00:03:45,000
+What do you call when you have a reference?
+
+98
+00:03:45,000 --> 00:03:47,000
+It is called a referenced object.
+
+99
+00:03:47,000 --> 00:03:49,000
+Okay, because there's a reference in this stack.
+
+100
+00:03:49,000 --> 00:03:51,000
+So when you say OBJ, there's a reference here.
+
+101
+00:03:51,000 --> 00:03:54,000
+For the anonymous object, there is no reference.
+
+102
+00:03:54,000 --> 00:03:56,000
+The only problem with this type of object is
+
+103
+00:03:56,000 --> 00:03:58,000
+you can't reuse them. Once you have written this line,
+
+104
+00:03:58,000 --> 00:04:02,000
+you got the new object in the heap, how will you use it?
+
+105
+00:04:02,000 --> 00:04:03,000
+That's the problem, right?
+
+106
+00:04:03,000 --> 00:04:04,000
+So you should use this type of object
+
+107
+00:04:04,000 --> 00:04:05,000
+only when it's required.
+
+108
+00:04:05,000 --> 00:04:08,000
+So let's say if you want to call show,
+
+109
+00:04:08,000 --> 00:04:09,000
+you can actually call this, okay?
+
+110
+00:04:09,000 --> 00:04:12,000
+So you can say new A,
+
+111
+00:04:12,000 --> 00:04:13,000
+dot show.
+
+112
+00:04:13,000 --> 00:04:15,000
+This is object, right? This is object.
+
+113
+00:04:15,000 --> 00:04:17,000
+So using the object you can call show.
+
+114
+00:04:17,000 --> 00:04:21,000
+The only thing is you can't use the same object again.
+
+115
+00:04:21,000 --> 00:04:24,000
+So if I compile and run, it worked.
+
+116
+00:04:24,000 --> 00:04:28,000
+The only thing is you can't use this object once more.
+
+117
+00:04:28,000 --> 00:04:30,000
+So if you write this line once more, what will happen?
+
+118
+00:04:30,000 --> 00:04:33,000
+Now, I mentioned that you can't reuse it.
+
+119
+00:04:33,000 --> 00:04:34,000
+What happens when you do that?
+
+120
+00:04:34,000 --> 00:04:36,000
+You can see it says object created.
+
+121
+00:04:36,000 --> 00:04:38,000
+So it has created two objects.
+
+122
+00:04:38,000 --> 00:04:43,000
+Every time you say new A, it creates a new object.
+
+123
+00:04:43,000 --> 00:04:45,000
+So wherever you want to use a normal object,
+
+124
+00:04:45,000 --> 00:04:47,000
+you can use this other objects.
+
+125
+00:04:47,000 --> 00:04:48,000
+Okay, so that's it.
+
+126
+00:04:48,000 --> 00:04:49,000
+That's it from this video
+
+127
+00:04:49,000 --> 00:04:51,000
+where we talked about anonymous objects.
+

02 - Core Java/050 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/051 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/051 What is Inheritance_en.srt

@@ -0,0 +1,848 @@
+1
+00:00:00,000 --> 00:00:02,000
+(gentle music)
+
+2
+00:00:03,000 --> 00:00:04,000
+-: So in theory, we have talked
+
+3
+00:00:04,000 --> 00:00:06,000
+about what is inheritance, right?
+
+4
+00:00:06,000 --> 00:00:09,000
+Basically, you can just use the features of a superclass.
+
+5
+00:00:09,000 --> 00:00:12,000
+Let's try to implement that in this code.
+
+6
+00:00:12,000 --> 00:00:13,000
+Of course, we'll not be working with Humans anymore.
+
+7
+00:00:13,000 --> 00:00:18,000
+Let me just remove the entire code from here, and all gone.
+
+8
+00:00:18,000 --> 00:00:22,000
+And let me also make sure that this is empty, gone.
+
+9
+00:00:22,000 --> 00:00:24,000
+So we have a very simple method, which is main here.
+
+10
+00:00:24,000 --> 00:00:26,000
+Now what I wanna do is I want
+
+11
+00:00:26,000 --> 00:00:28,000
+to take the same example of calculator here.
+
+12
+00:00:28,000 --> 00:00:30,000
+So let me get a class called Calc,
+
+13
+00:00:30,000 --> 00:00:32,000
+and of course, I can just create this thing
+
+14
+00:00:32,000 --> 00:00:35,000
+in some other files as well, that actually makes sense.
+
+15
+00:00:35,000 --> 00:00:39,000
+But just to keep it simple, I'm using the same file here.
+
+16
+00:00:39,000 --> 00:00:41,000
+So we got a class called calculator,
+
+17
+00:00:41,000 --> 00:00:43,000
+and in this, I can add some methods and some variables.
+
+18
+00:00:43,000 --> 00:00:46,000
+So let's say I will define some methods here,
+
+19
+00:00:46,000 --> 00:00:49,000
+and I'll say public int, it can add two numbers.
+
+20
+00:00:49,000 --> 00:00:53,000
+It will accept two integers as well, I would say n1, n2.
+
+21
+00:00:53,000 --> 00:00:55,000
+So we got two variables, right?
+
+22
+00:00:55,000 --> 00:01:00,000
+And then I can just return n1 + n2, okay?
+
+23
+00:01:00,000 --> 00:01:03,000
+Now let's say in this calculator, we have two methods.
+
+24
+00:01:03,000 --> 00:01:08,000
+One is add and one is sub, which is sub here.
+
+25
+00:01:08,000 --> 00:01:09,000
+And there will be a subtraction operation.
+
+26
+00:01:09,000 --> 00:01:11,000
+So we got two methods, right?
+
+27
+00:01:11,000 --> 00:01:14,000
+Now one thing to remember, if you look at our File Explorer,
+
+28
+00:01:14,000 --> 00:01:17,000
+every time you get a file, it also creates a class file.
+
+29
+00:01:17,000 --> 00:01:20,000
+So for every class in your code, it will have a class files.
+
+30
+00:01:20,000 --> 00:01:24,000
+We have used a Calculator, a Computer,
+
+31
+00:01:24,000 --> 00:01:25,000
+Human, Student before,
+
+32
+00:01:25,000 --> 00:01:27,000
+and that's why we have all these classes.
+
+33
+00:01:27,000 --> 00:01:29,000
+What I will do is I will just delete them.
+
+34
+00:01:29,000 --> 00:01:31,000
+Okay, so you can see all these classes are gone.
+
+35
+00:01:31,000 --> 00:01:33,000
+In fact, let me also delete the Demo one
+
+36
+00:01:33,000 --> 00:01:34,000
+to see what happens.
+
+37
+00:01:34,000 --> 00:01:36,000
+And that's fine, you can also delete,
+
+38
+00:01:36,000 --> 00:01:37,000
+you can delete all the class files.
+
+39
+00:01:37,000 --> 00:01:39,000
+So every time you compile the code,
+
+40
+00:01:39,000 --> 00:01:40,000
+it will also create a class files for you.
+
+41
+00:01:40,000 --> 00:01:42,000
+Let me show you that.
+
+42
+00:01:42,000 --> 00:01:45,000
+So I will say javac, and if I mention the file name,
+
+43
+00:01:45,000 --> 00:01:49,000
+which is Demo.java, the moment I say Enter,
+
+44
+00:01:49,000 --> 00:01:50,000
+it will create two class files
+
+45
+00:01:50,000 --> 00:01:51,000
+because we have two classes.
+
+46
+00:01:51,000 --> 00:01:55,000
+If I go to Explorer, you can see we got Demo.class,
+
+47
+00:01:55,000 --> 00:01:57,000
+and we also have Calc.class.
+
+48
+00:01:57,000 --> 00:01:59,000
+Now when you run this code, if you say java,
+
+49
+00:01:59,000 --> 00:02:02,000
+and if you say Demo, it will just run the class files.
+
+50
+00:02:02,000 --> 00:02:04,000
+And as you can see,
+
+51
+00:02:04,000 --> 00:02:07,000
+we don't have any code here for calculator.
+
+52
+00:02:07,000 --> 00:02:11,000
+It will only run the Demo class, and that's how it works.
+
+53
+00:02:11,000 --> 00:02:14,000
+So if I just try to write this code here,
+
+54
+00:02:14,000 --> 00:02:18,000
+which we already have, and if I try to create object of it,
+
+55
+00:02:18,000 --> 00:02:19,000
+let's try creating object of it.
+
+56
+00:02:19,000 --> 00:02:22,000
+In fact, let me do one more thing before we start.
+
+57
+00:02:22,000 --> 00:02:25,000
+For this example, let me cut this part,
+
+58
+00:02:25,000 --> 00:02:30,000
+and create a new file and let me say this is Calc.java.
+
+59
+00:02:31,000 --> 00:02:35,000
+And yes, we have this code here.
+
+60
+00:02:35,000 --> 00:02:37,000
+So you can see now we have two files, and before I continue,
+
+61
+00:02:37,000 --> 00:02:40,000
+I will just delete these class files again.
+
+62
+00:02:40,000 --> 00:02:41,000
+Okay, class file deleted.
+
+63
+00:02:41,000 --> 00:02:45,000
+And now let me just compile this code once again.
+
+64
+00:02:45,000 --> 00:02:47,000
+So if you can see when I'm compiling it,
+
+65
+00:02:47,000 --> 00:02:50,000
+it is only compiling the Demo file.
+
+66
+00:02:50,000 --> 00:02:53,000
+It is not combining the class.java, right?
+
+67
+00:02:53,000 --> 00:02:55,000
+But when I create an object of it,
+
+68
+00:02:55,000 --> 00:02:58,000
+if I create object of Calc obj = new Calc,
+
+69
+00:02:58,000 --> 00:03:00,000
+of course if you want to use it,
+
+70
+00:03:00,000 --> 00:03:02,000
+we have to create object first.
+
+71
+00:03:02,000 --> 00:03:04,000
+And now if I recompile this,
+
+72
+00:03:04,000 --> 00:03:06,000
+and let's look at the class files.
+
+73
+00:03:06,000 --> 00:03:08,000
+We got the class file for class as well.
+
+74
+00:03:08,000 --> 00:03:12,000
+So if you are not using Calc, it will not compile it.
+
+75
+00:03:12,000 --> 00:03:13,000
+It'll just say, "Hey,
+
+76
+00:03:13,000 --> 00:03:15,000
+my responsibility is to compile the Java file.
+
+77
+00:03:15,000 --> 00:03:16,000
+I'm doing it."
+
+78
+00:03:16,000 --> 00:03:18,000
+But if you want to work with the class,
+
+79
+00:03:18,000 --> 00:03:21,000
+the Calc.class as well, or Calc.java as well,
+
+80
+00:03:21,000 --> 00:03:25,000
+you have to create object and that's how it compiles.
+
+81
+00:03:25,000 --> 00:03:26,000
+Now once the compile is done,
+
+82
+00:03:26,000 --> 00:03:30,000
+you can simply save the value in r1 or you can say obj.add.
+
+83
+00:03:30,000 --> 00:03:33,000
+It will add two numbers, let's say four and five.
+
+84
+00:03:33,000 --> 00:03:35,000
+And then we can also find r2,
+
+85
+00:03:35,000 --> 00:03:37,000
+which will be result of subtraction.
+
+86
+00:03:37,000 --> 00:03:41,000
+So I can say sub, I will say seven and three, okay?
+
+87
+00:03:41,000 --> 00:03:43,000
+So we basically, you can see we got these two methods,
+
+88
+00:03:43,000 --> 00:03:45,000
+and when you try to print the values,
+
+89
+00:03:45,000 --> 00:03:48,000
+I will print r1 and I will give us space,
+
+90
+00:03:48,000 --> 00:03:49,000
+and I'll also print r2.
+
+91
+00:03:49,000 --> 00:03:51,000
+So basically, I'm just printing two values back to back.
+
+92
+00:03:51,000 --> 00:03:55,000
+And if I say compile again because we have made some changes
+
+93
+00:03:55,000 --> 00:03:57,000
+and run, you can see we got nine and four.
+
+94
+00:03:57,000 --> 00:04:00,000
+So 4 + 5 is nine, 7 - 3 is four,
+
+95
+00:04:00,000 --> 00:04:02,000
+and that's what we are getting here.
+
+96
+00:04:02,000 --> 00:04:03,000
+Everything is working fine, right?
+
+97
+00:04:03,000 --> 00:04:05,000
+Now there are two conditions here,
+
+98
+00:04:05,000 --> 00:04:06,000
+why we are going for inheritance.
+
+99
+00:04:06,000 --> 00:04:09,000
+The first one is what if you want
+
+100
+00:04:09,000 --> 00:04:10,000
+to add some extra features?
+
+101
+00:04:10,000 --> 00:04:13,000
+You want, so let's say if someone is asking you for,
+
+102
+00:04:13,000 --> 00:04:14,000
+"Hey, you know, Navin,
+
+103
+00:04:14,000 --> 00:04:17,000
+I want a calculator and I want two features,
+
+104
+00:04:17,000 --> 00:04:19,000
+addition and subtraction.
+
+105
+00:04:19,000 --> 00:04:20,000
+What will be the cost?"
+
+106
+00:04:20,000 --> 00:04:22,000
+I would say, "Okay, I will charge you $10."
+
+107
+00:04:22,000 --> 00:04:24,000
+Now let's say the same person come back and say,
+
+108
+00:04:24,000 --> 00:04:27,000
+"Hey, you know, I want a calculator which has four features,
+
+109
+00:04:27,000 --> 00:04:29,000
+additional, subtraction, division, multiplication."
+
+110
+00:04:29,000 --> 00:04:33,000
+And maybe at this point, I want to charge $15.
+
+111
+00:04:33,000 --> 00:04:35,000
+Now of course, I can add those two methods here
+
+112
+00:04:35,000 --> 00:04:38,000
+or I can create a new class, you know why?
+
+113
+00:04:38,000 --> 00:04:41,000
+It's because if I edit the same file,
+
+114
+00:04:41,000 --> 00:04:42,000
+if I add more features here,
+
+115
+00:04:42,000 --> 00:04:45,000
+I can't sell calculator for $10 now.
+
+116
+00:04:45,000 --> 00:04:47,000
+I have to make a new product for $15.
+
+117
+00:04:47,000 --> 00:04:49,000
+I don't have calculator,
+
+118
+00:04:49,000 --> 00:04:51,000
+I have advanced calculator which does four operations.
+
+119
+00:04:51,000 --> 00:04:52,000
+I want both the models.
+
+120
+00:04:52,000 --> 00:04:57,000
+I want to sell the $10 calculator and a $15 calculator.
+
+121
+00:04:57,000 --> 00:04:59,000
+That's one reason. Okay, so let me just do that.
+
+122
+00:04:59,000 --> 00:05:01,000
+So let me create a new calculator,
+
+123
+00:05:01,000 --> 00:05:04,000
+and I will say this is advanced calculator,
+
+124
+00:05:04,000 --> 00:05:07,000
+which has all the features, .java.
+
+125
+00:05:07,000 --> 00:05:10,000
+And in this, I will basically have two more methods,
+
+126
+00:05:10,000 --> 00:05:15,000
+which is public int multi, which will take two values,
+
+127
+00:05:15,000 --> 00:05:19,000
+and it should return n1 into n2.
+
+128
+00:05:19,000 --> 00:05:21,000
+And likewise, we'll have one more method here for division.
+
+129
+00:05:21,000 --> 00:05:26,000
+So this is div and division, we have to say slash.
+
+130
+00:05:26,000 --> 00:05:28,000
+That's it, so we got an advanced calculator,
+
+131
+00:05:28,000 --> 00:05:29,000
+which has two features.
+
+132
+00:05:29,000 --> 00:05:33,000
+But now if I create an object of advanced calculator now,
+
+133
+00:05:33,000 --> 00:05:35,000
+instead of normal calculator,
+
+134
+00:05:35,000 --> 00:05:37,000
+I can access multiplication and division.
+
+135
+00:05:37,000 --> 00:05:39,000
+I can't access add and sub.
+
+136
+00:05:39,000 --> 00:05:41,000
+And that's why you can see we got an error here.
+
+137
+00:05:41,000 --> 00:05:44,000
+It says, "The method add is undefined
+
+138
+00:05:44,000 --> 00:05:46,000
+for type advanced calculator."
+
+139
+00:05:46,000 --> 00:05:48,000
+That means in this, we don't have add and subtract.
+
+140
+00:05:48,000 --> 00:05:50,000
+So what do you think? What could be solution here?
+
+141
+00:05:50,000 --> 00:05:52,000
+Think about this, so one solution,
+
+142
+00:05:52,000 --> 00:05:56,000
+which I can see is just write those two methods here.
+
+143
+00:05:56,000 --> 00:05:57,000
+Of course, we can do that.
+
+144
+00:05:57,000 --> 00:05:59,000
+Okay, we can just copy and we can paste it here.
+
+145
+00:05:59,000 --> 00:06:01,000
+But don't you think we are writing
+
+146
+00:06:01,000 --> 00:06:04,000
+the same code again and again?
+
+147
+00:06:04,000 --> 00:06:05,000
+Now when you repeat the same code,
+
+148
+00:06:05,000 --> 00:06:07,000
+it is called redundancy, right?
+
+149
+00:06:07,000 --> 00:06:12,000
+We have same code multiple times, and redundancy is a crime.
+
+150
+00:06:12,000 --> 00:06:13,000
+So make sure that you don't repeat the values,
+
+151
+00:06:13,000 --> 00:06:17,000
+you don't repeat the methods, definition, and classes.
+
+152
+00:06:17,000 --> 00:06:19,000
+The point is if I don't define it here,
+
+153
+00:06:19,000 --> 00:06:21,000
+how will I access them?
+
+154
+00:06:21,000 --> 00:06:24,000
+That's where the in inheritance concept comes into picture.
+
+155
+00:06:24,000 --> 00:06:26,000
+So in inheritance says, "Hey, don't worry.
+
+156
+00:06:26,000 --> 00:06:28,000
+If you already have a class called Calc,
+
+157
+00:06:28,000 --> 00:06:31,000
+you can simply say extends Calc, your job is done."
+
+158
+00:06:31,000 --> 00:06:34,000
+Okay, so you simply say advanced calculator
+
+159
+00:06:34,000 --> 00:06:37,000
+extends calculator, and now all the features
+
+160
+00:06:37,000 --> 00:06:40,000
+of calculator comes in here.
+
+161
+00:06:40,000 --> 00:06:41,000
+And there's one more beauty.
+
+162
+00:06:41,000 --> 00:06:44,000
+Even if you don't have this Java file, that's fine.
+
+163
+00:06:44,000 --> 00:06:48,000
+For inheritance, you need a class file, not a Java file.
+
+164
+00:06:48,000 --> 00:06:50,000
+So even if you delete this, it will still work, okay?
+
+165
+00:06:50,000 --> 00:06:51,000
+That's the first reason.
+
+166
+00:06:51,000 --> 00:06:53,000
+Even if you don't have a code ready with you,
+
+167
+00:06:53,000 --> 00:06:55,000
+even if you don't have a Java file,
+
+168
+00:06:55,000 --> 00:06:57,000
+you can still use a class file.
+
+169
+00:06:57,000 --> 00:06:59,000
+Okay, so that's the beauty of inheritance.
+
+170
+00:06:59,000 --> 00:07:01,000
+We are simply saying extends calculator,
+
+171
+00:07:01,000 --> 00:07:02,000
+which is this class.
+
+172
+00:07:02,000 --> 00:07:05,000
+Now what do you think, will it work? Let's try.
+
+173
+00:07:05,000 --> 00:07:06,000
+So you can see there's no problem,
+
+174
+00:07:06,000 --> 00:07:07,000
+add and subtraction working.
+
+175
+00:07:07,000 --> 00:07:09,000
+We can add some more variables here.
+
+176
+00:07:09,000 --> 00:07:13,000
+I can just copy this code and paste, paste,
+
+177
+00:07:13,000 --> 00:07:14,000
+not on the same line.
+
+178
+00:07:15,000 --> 00:07:18,000
+This is my r3, this is my r4,
+
+179
+00:07:18,000 --> 00:07:21,000
+and I can just say this is multiplication.
+
+180
+00:07:21,000 --> 00:07:23,000
+Okay, so multiplying number,
+
+181
+00:07:23,000 --> 00:07:27,000
+like let's say is five and three, okay?
+
+182
+00:07:27,000 --> 00:07:29,000
+And then dividing the number,
+
+183
+00:07:29,000 --> 00:07:33,000
+let's say 15 by 4.
+
+184
+00:07:33,000 --> 00:07:36,000
+Let's do this, and now when I perform this operation,
+
+185
+00:07:36,000 --> 00:07:39,000
+of course, I want to print r3 and r4 as well
+
+186
+00:07:39,000 --> 00:07:40,000
+on the same line.
+
+187
+00:07:40,000 --> 00:07:43,000
+I'm lazy to write multiple lines of code here, and r4.
+
+188
+00:07:43,000 --> 00:07:46,000
+So we are printing everything in the same line.
+
+189
+00:07:46,000 --> 00:07:48,000
+Let's try what happens.
+
+190
+00:07:48,000 --> 00:07:51,000
+Compile, no problem. Run, it works.
+
+191
+00:07:51,000 --> 00:07:54,000
+Can see that addition is nine, subtraction is four,
+
+192
+00:07:54,000 --> 00:07:56,000
+multiplication is 15, if I'm not wrong, yeah,
+
+193
+00:07:56,000 --> 00:07:58,000
+and division is three.
+
+194
+00:07:58,000 --> 00:08:02,000
+So 15 divided by four will give you a quotient of three.
+
+195
+00:08:02,000 --> 00:08:03,000
+Okay, cool, this is working right?
+
+196
+00:08:03,000 --> 00:08:06,000
+So this is how we use inheritance.
+
+197
+00:08:06,000 --> 00:08:10,000
+So important thing here is this advanced calculator
+
+198
+00:08:10,000 --> 00:08:11,000
+here is called a subclass.
+
+199
+00:08:11,000 --> 00:08:14,000
+This calculator here is called a superclass.
+
+200
+00:08:14,000 --> 00:08:18,000
+And to inherit, we use a keyword called extends, okay?
+
+201
+00:08:18,000 --> 00:08:22,000
+And this is basically a relationship of is-a.
+
+202
+00:08:22,000 --> 00:08:26,000
+Advanced calculator is a calculator,
+
+203
+00:08:26,000 --> 00:08:28,000
+and that's why we say is, an important word there.
+
+204
+00:08:28,000 --> 00:08:31,000
+Cool, can I have multiple classes in hitting each other?
+
+205
+00:08:31,000 --> 00:08:33,000
+We can, that's we'll see in the upcoming videos.
+
+206
+00:08:33,000 --> 00:08:36,000
+At this point, we just went for a simple inheritance
+
+207
+00:08:36,000 --> 00:08:39,000
+where we just use the feature of a superclass.
+
+208
+00:08:39,000 --> 00:08:41,000
+You can say parent has all these two features,
+
+209
+00:08:41,000 --> 00:08:44,000
+child is just extending it or using it.
+
+210
+00:08:44,000 --> 00:08:46,000
+I can say this is nepotism.
+
+211
+00:08:46,000 --> 00:08:47,000
+(laughs) So that's it from this video.
+
+212
+00:08:47,000 --> 00:08:50,000
+I hope you enjoyed and see you in the next video.
+

02 - Core Java/052 Need of Inheritance_en.srt

@@ -0,0 +1,664 @@
+1
+00:00:00,000 --> 00:00:03,000
+(bright music)
+
+2
+00:00:03,000 --> 00:00:05,000
+-: Now let's talk more about OOPs concept.
+
+3
+00:00:05,000 --> 00:00:09,000
+Now, OOPs basically stands for Object Oriented Programming.
+
+4
+00:00:09,000 --> 00:00:10,000
+Now, in Object Oriented Programming,
+
+5
+00:00:10,000 --> 00:00:14,000
+we have talked about Object Class Encapsulation, right?
+
+6
+00:00:14,000 --> 00:00:16,000
+Now let's talk more concepts.
+
+7
+00:00:16,000 --> 00:00:17,000
+Now, one of the most important thing
+
+8
+00:00:17,000 --> 00:00:21,000
+in the concept of OOPs is called inheritance.
+
+9
+00:00:21,000 --> 00:00:23,000
+Now, what is inheritance?
+
+10
+00:00:23,000 --> 00:00:25,000
+Now, there are two words actually here,
+
+11
+00:00:25,000 --> 00:00:30,000
+which will confuse people is, "is" and "has."
+
+12
+00:00:30,000 --> 00:00:32,000
+Now what these two words are.
+
+13
+00:00:32,000 --> 00:00:33,000
+Now, if we talk about a computer,
+
+14
+00:00:33,000 --> 00:00:36,000
+now, of course, computer itself is abstract concept, right?
+
+15
+00:00:36,000 --> 00:00:39,000
+Now a computer can be a laptop, a computer can be a desktop,
+
+16
+00:00:39,000 --> 00:00:41,000
+a computer can be a mobile phone.
+
+17
+00:00:41,000 --> 00:00:42,000
+That's right.
+
+18
+00:00:42,000 --> 00:00:43,000
+So even if you talk about this phone,
+
+19
+00:00:43,000 --> 00:00:47,000
+this is a computer in the form of mobile phone, of course.
+
+20
+00:00:47,000 --> 00:00:49,000
+And the computer itself is an abstract concept.
+
+21
+00:00:49,000 --> 00:00:50,000
+No one owns a computer.
+
+22
+00:00:50,000 --> 00:00:52,000
+You basically buy a hardware,
+
+23
+00:00:52,000 --> 00:00:54,000
+which can be a desktop, laptop, or a phone.
+
+24
+00:00:54,000 --> 00:00:57,000
+Now, can I say that if you talk about a desktop,
+
+25
+00:00:57,000 --> 00:00:58,000
+so I'm talking about a desktop, which is this big,
+
+26
+00:00:58,000 --> 00:01:01,000
+and it will have certain parts, right?
+
+27
+00:01:01,000 --> 00:01:02,000
+A desktop will have a motherboard,
+
+28
+00:01:02,000 --> 00:01:05,000
+a desktop will have a hard drive, CPU, ram.
+
+29
+00:01:05,000 --> 00:01:06,000
+So when you talk about this thing,
+
+30
+00:01:06,000 --> 00:01:10,000
+it is desktop has a motherboard,
+
+31
+00:01:10,000 --> 00:01:14,000
+desktop has a hard drive, it has a CPU, right?
+
+32
+00:01:14,000 --> 00:01:16,000
+So the important keyword there is "has."
+
+33
+00:01:16,000 --> 00:01:19,000
+If we talk about a house, a house will have a TV,
+
+34
+00:01:19,000 --> 00:01:22,000
+a house will have a sofa, AC, bed.
+
+35
+00:01:22,000 --> 00:01:25,000
+So all those things, what a house has, right?
+
+36
+00:01:25,000 --> 00:01:27,000
+So "has" is an important word.
+
+37
+00:01:27,000 --> 00:01:28,000
+But at this point, let's not focus on "has."
+
+38
+00:01:28,000 --> 00:01:30,000
+In this video, let's talk about "is."
+
+39
+00:01:30,000 --> 00:01:32,000
+Now what is, is, is.
+
+40
+00:01:32,000 --> 00:01:34,000
+Okay, so example, if we talk about a laptop,
+
+41
+00:01:34,000 --> 00:01:38,000
+so can we say a laptop is a computer?
+
+42
+00:01:38,000 --> 00:01:42,000
+So what it means is, laptop got it features from a computer.
+
+43
+00:01:42,000 --> 00:01:44,000
+So can we take another example here?
+
+44
+00:01:44,000 --> 00:01:46,000
+If we talk about a car, let's say.
+
+45
+00:01:46,000 --> 00:01:48,000
+Let's say if we talk about a Fortuner,
+
+46
+00:01:48,000 --> 00:01:49,000
+which is very famous in India.
+
+47
+00:01:49,000 --> 00:01:51,000
+So this car is actually a car, right?
+
+48
+00:01:51,000 --> 00:01:54,000
+So Fortuner is a car.
+
+49
+00:01:54,000 --> 00:01:55,000
+So that's how you represent something.
+
+50
+00:01:55,000 --> 00:01:58,000
+You represent a device or a physical entity
+
+51
+00:01:58,000 --> 00:02:00,000
+by referring to its upper model,
+
+52
+00:02:00,000 --> 00:02:02,000
+or you try to take the features of it.
+
+53
+00:02:02,000 --> 00:02:04,000
+Now, coming back to the Inheritance concept,
+
+54
+00:02:04,000 --> 00:02:06,000
+in real world example,
+
+55
+00:02:06,000 --> 00:02:08,000
+let's say if we talk about the human world,
+
+56
+00:02:08,000 --> 00:02:10,000
+you know, when I was in my 10th standard,
+
+57
+00:02:10,000 --> 00:02:12,000
+so just for the example, okay, not that important,
+
+58
+00:02:12,000 --> 00:02:16,000
+but when I was in my 10th standard, I did my 10th in 2005.
+
+59
+00:02:16,000 --> 00:02:20,000
+At that point, Nokia released a lot of smartphones, right?
+
+60
+00:02:20,000 --> 00:02:21,000
+Of course, Nokia is not there anymore,
+
+61
+00:02:21,000 --> 00:02:25,000
+but Nokia was one of the most important factor
+
+62
+00:02:25,000 --> 00:02:26,000
+in the smartphone industry.
+
+63
+00:02:26,000 --> 00:02:28,000
+Now, when they came up with a smartphone,
+
+64
+00:02:28,000 --> 00:02:31,000
+one of the most famous smartphone which they built is 6600.
+
+65
+00:02:31,000 --> 00:02:33,000
+I'm not sure if you have seen that.
+
+66
+00:02:33,000 --> 00:02:34,000
+I'm not even sure if you're that old.
+
+67
+00:02:34,000 --> 00:02:37,000
+Maybe you were not even born in that year.
+
+68
+00:02:37,000 --> 00:02:39,000
+But yeah, so it was 6600. Amazing phone.
+
+69
+00:02:39,000 --> 00:02:42,000
+If you can just search on Google, Nokia 6600,
+
+70
+00:02:42,000 --> 00:02:44,000
+you will see that phone.
+
+71
+00:02:44,000 --> 00:02:46,000
+Now, a lot of my friends were having that phone.
+
+72
+00:02:46,000 --> 00:02:47,000
+It was costly phone at that point.
+
+73
+00:02:47,000 --> 00:02:49,000
+It was around 10,000 rupees.
+
+74
+00:02:49,000 --> 00:02:51,000
+And I was not having any phone.
+
+75
+00:02:51,000 --> 00:02:52,000
+So they used to ask me, "Hey, which phone you have?"
+
+76
+00:02:52,000 --> 00:02:54,000
+I used to say, "Hey, I don't have a phone."
+
+77
+00:02:54,000 --> 00:02:58,000
+But then I realized, hey, till when I will say that.
+
+78
+00:02:58,000 --> 00:02:59,000
+The thing is,
+
+79
+00:02:59,000 --> 00:03:01,000
+next time when people used to ask me which phone I have,
+
+80
+00:03:01,000 --> 00:03:04,000
+I used to say I have 3310.
+
+81
+00:03:04,000 --> 00:03:05,000
+Now, I was not having any phone.
+
+82
+00:03:05,000 --> 00:03:07,000
+Now, this is my father's phone,
+
+83
+00:03:07,000 --> 00:03:09,000
+and we know the concept, right?
+
+84
+00:03:09,000 --> 00:03:10,000
+Father's phone is yours phone.
+
+85
+00:03:10,000 --> 00:03:12,000
+In fact, in general, we say,
+
+86
+00:03:12,000 --> 00:03:14,000
+our parents' property, it's your property.
+
+87
+00:03:14,000 --> 00:03:16,000
+Whatever they own, it's yours.
+
+88
+00:03:16,000 --> 00:03:17,000
+I don't believe in that, okay?
+
+89
+00:03:17,000 --> 00:03:20,000
+I'm not a big fan of inheritance or nepotism,
+
+90
+00:03:20,000 --> 00:03:22,000
+but yeah, you get everything.
+
+91
+00:03:22,000 --> 00:03:24,000
+So I used to say I have that phone.
+
+92
+00:03:24,000 --> 00:03:25,000
+Okay, so this is inheritance.
+
+93
+00:03:25,000 --> 00:03:27,000
+Now, how will you use this concept in programming?
+
+94
+00:03:27,000 --> 00:03:29,000
+Now in Java, what you have
+
+95
+00:03:29,000 --> 00:03:30,000
+is you have different classes, right?
+
+96
+00:03:30,000 --> 00:03:32,000
+Example, if you create a simple class here.
+
+97
+00:03:32,000 --> 00:03:33,000
+Let me get a very simple class.
+
+98
+00:03:33,000 --> 00:03:36,000
+Let's say we have a class here called Calculator.
+
+99
+00:03:36,000 --> 00:03:38,000
+Now what features a calculator will have?
+
+100
+00:03:38,000 --> 00:03:41,000
+A calculator will have some variables here,
+
+101
+00:03:41,000 --> 00:03:42,000
+and then it will have some methods.
+
+102
+00:03:42,000 --> 00:03:46,000
+Let's say method is add, a method is sub, okay?
+
+103
+00:03:46,000 --> 00:03:48,000
+And then method is multi.
+
+104
+00:03:48,000 --> 00:03:50,000
+So we have different methods here.
+
+105
+00:03:50,000 --> 00:03:51,000
+And let's also have division.
+
+106
+00:03:51,000 --> 00:03:53,000
+Why division should be left there?
+
+107
+00:03:53,000 --> 00:03:56,000
+So we have all these methods, right? And it is working.
+
+108
+00:03:56,000 --> 00:03:58,000
+So you can basically create object of Calculator,
+
+109
+00:03:58,000 --> 00:03:59,000
+and you can access all these methods.
+
+110
+00:03:59,000 --> 00:04:00,000
+No harm in that.
+
+111
+00:04:00,000 --> 00:04:04,000
+But what if you want to create a advanced calculator?
+
+112
+00:04:04,000 --> 00:04:06,000
+Now of course, let's say if someone comes to you
+
+113
+00:04:06,000 --> 00:04:09,000
+and say, "Hey, you know, you made a awesome calculator
+
+114
+00:04:09,000 --> 00:04:12,000
+and now I want you to create a scientific calculator
+
+115
+00:04:12,000 --> 00:04:14,000
+or advanced calculator."
+
+116
+00:04:14,000 --> 00:04:15,000
+Now you have a choice.
+
+117
+00:04:15,000 --> 00:04:18,000
+You can edit the same class, but there's only one thing.
+
+118
+00:04:18,000 --> 00:04:20,000
+What if you enhance the same class?
+
+119
+00:04:20,000 --> 00:04:21,000
+You add some more methods here.
+
+120
+00:04:21,000 --> 00:04:25,000
+Now you want to give Calculator to someone,
+
+121
+00:04:25,000 --> 00:04:27,000
+someone asking you for the Calculator object.
+
+122
+00:04:27,000 --> 00:04:28,000
+They basically access all the basic features
+
+123
+00:04:28,000 --> 00:04:30,000
+and advanced features, as well.
+
+124
+00:04:30,000 --> 00:04:33,000
+So it is good to create a separate class, okay?
+
+125
+00:04:33,000 --> 00:04:34,000
+So you can get a separate class,
+
+126
+00:04:34,000 --> 00:04:37,000
+and you can say Advanced Calculator, right?
+
+127
+00:04:37,000 --> 00:04:40,000
+And then this will have all the advanced features.
+
+128
+00:04:40,000 --> 00:04:41,000
+Of course, it will have all the basic features,
+
+129
+00:04:41,000 --> 00:04:43,000
+and it will have the advanced features, as well.
+
+130
+00:04:43,000 --> 00:04:46,000
+So we have basic features, advanced features both.
+
+131
+00:04:46,000 --> 00:04:47,000
+But don't you think
+
+132
+00:04:47,000 --> 00:04:51,000
+you need to define these basic features again and again?
+
+133
+00:04:51,000 --> 00:04:54,000
+Why? We already have those features here, right?
+
+134
+00:04:54,000 --> 00:04:56,000
+We already have those features here.
+
+135
+00:04:56,000 --> 00:05:01,000
+Can I just use those features in my new Advanced Calculator?
+
+136
+00:05:02,000 --> 00:05:04,000
+So what I'm saying is basically
+
+137
+00:05:04,000 --> 00:05:07,000
+this Advanced Calculator is going to inherit
+
+138
+00:05:07,000 --> 00:05:12,000
+the properties and features from Calculator.
+
+139
+00:05:12,000 --> 00:05:15,000
+So I can also say Advanced Calculator is a Calculator,
+
+140
+00:05:15,000 --> 00:05:17,000
+and it will get all the features of Calculator.
+
+141
+00:05:17,000 --> 00:05:20,000
+Okay, it will make much more sense once we start coding.
+
+142
+00:05:20,000 --> 00:05:24,000
+But what we are doing here is, we are doing inheritance.
+
+143
+00:05:24,000 --> 00:05:27,000
+So basically, inheritance is a very important feature,
+
+144
+00:05:27,000 --> 00:05:29,000
+using which you can just copy the feature
+
+145
+00:05:29,000 --> 00:05:31,000
+from the upper class.
+
+146
+00:05:31,000 --> 00:05:32,000
+Can I say this is a parent class?
+
+147
+00:05:32,000 --> 00:05:37,000
+So this is a parent class, and this is a child class
+
+148
+00:05:37,000 --> 00:05:39,000
+because child class is accessing
+
+149
+00:05:39,000 --> 00:05:41,000
+the feature of parent class, okay?
+
+150
+00:05:41,000 --> 00:05:44,000
+So whatever I earn, it's my money,
+
+151
+00:05:44,000 --> 00:05:45,000
+plus my parent's money is my money.
+
+152
+00:05:45,000 --> 00:05:46,000
+That's how the system works, right?
+
+153
+00:05:46,000 --> 00:05:49,000
+We can also say this is a super class.
+
+154
+00:05:49,000 --> 00:05:51,000
+We have different words for it. That's it.
+
+155
+00:05:51,000 --> 00:05:54,000
+And we can say this is a subclass.
+
+156
+00:05:54,000 --> 00:05:57,000
+We can also say this is a base class, base.
+
+157
+00:05:57,000 --> 00:06:00,000
+And this is a derived class.
+
+158
+00:06:00,000 --> 00:06:02,000
+So it depends upon how you represent that.
+
+159
+00:06:02,000 --> 00:06:04,000
+If you say this is a parent class,
+
+160
+00:06:04,000 --> 00:06:06,000
+then you have to say it's a child class.
+
+161
+00:06:06,000 --> 00:06:09,000
+If you say that's a super class, then it becomes a subclass.
+
+162
+00:06:09,000 --> 00:06:09,000
+If you say this is a base class,
+
+163
+00:06:09,000 --> 00:06:11,000
+you have to say this is a derived class.
+
+164
+00:06:11,000 --> 00:06:13,000
+That's how it works, okay?
+
+165
+00:06:13,000 --> 00:06:16,000
+Now, this is what inheritance is.
+
+166
+00:06:16,000 --> 00:06:19,000
+Now we'll try to implement this in code in the next video.
+

02 - Core Java/052 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/053 Single and Multilevel inheritance_en.srt

@@ -0,0 +1,396 @@
+1
+00:00:00,000 --> 00:00:03,000
+(piano music opening)
+
+2
+00:00:03,000 --> 00:00:06,000
+-: So basically we were able to do advanced calculator,
+
+3
+00:00:06,000 --> 00:00:08,000
+which uses a feature of calculator, right?
+
+4
+00:00:08,000 --> 00:00:10,000
+So this is extends.
+
+5
+00:00:10,000 --> 00:00:12,000
+Now what if in future,
+
+6
+00:00:12,000 --> 00:00:15,000
+let's say we got one more requirement, we want to build a,
+
+7
+00:00:15,000 --> 00:00:16,000
+let's say scientific calculator
+
+8
+00:00:16,000 --> 00:00:17,000
+and I don't know the operation,
+
+9
+00:00:17,000 --> 00:00:20,000
+so I will just say Very Advanced Calculator.
+
+10
+00:00:20,000 --> 00:00:23,000
+I'm very bad with names, so I will just use this
+
+11
+00:00:23,000 --> 00:00:26,000
+and this advanced calculator will have extra feature.
+
+12
+00:00:26,000 --> 00:00:27,000
+Let's say it also has a feature
+
+13
+00:00:27,000 --> 00:00:31,000
+of finding the power of a number.
+
+14
+00:00:31,000 --> 00:00:33,000
+Okay? So let's say public int,
+
+15
+00:00:33,000 --> 00:00:34,000
+I can simply say, yeah, power.
+
+16
+00:00:34,000 --> 00:00:37,000
+Now what we power, let's say three is two. I wanna do that.
+
+17
+00:00:37,000 --> 00:00:38,000
+So it'll take two numbers.
+
+18
+00:00:38,000 --> 00:00:40,000
+The first value N1,
+
+19
+00:00:40,000 --> 00:00:43,000
+and I also want a power, let's say N2
+
+20
+00:00:43,000 --> 00:00:44,000
+and let's say this will return, okay?
+
+21
+00:00:44,000 --> 00:00:47,000
+How do we do the power? So basically we have a math class.
+
+22
+00:00:47,000 --> 00:00:49,000
+I can just simply use it.
+
+23
+00:00:49,000 --> 00:00:52,000
+Math., yeah, we have a function of power.
+
+24
+00:00:52,000 --> 00:00:55,000
+Just take double value, but that's fine. I will just pass.
+
+25
+00:00:55,000 --> 00:00:57,000
+Integer double also takes integer value.
+
+26
+00:00:57,000 --> 00:00:58,000
+N1, N2.
+
+27
+00:00:58,000 --> 00:01:01,000
+And the problem is it also returns the double value.
+
+28
+00:01:01,000 --> 00:01:03,000
+If you can see, power returns are double value.
+
+29
+00:01:03,000 --> 00:01:06,000
+So what I will do is, let me return double value, okay?
+
+30
+00:01:06,000 --> 00:01:08,000
+So you have a choice, you can return double value
+
+31
+00:01:08,000 --> 00:01:12,000
+or you can just typecast it with int and you can do that.
+
+32
+00:01:12,000 --> 00:01:13,000
+Otherwise double is okay.
+
+33
+00:01:13,000 --> 00:01:14,000
+So you can see we have a power function,
+
+34
+00:01:14,000 --> 00:01:17,000
+which takes this method and it calculates.
+
+35
+00:01:17,000 --> 00:01:19,000
+Now the thing is, if I want to create
+
+36
+00:01:19,000 --> 00:01:21,000
+object of power, well I will do that.
+
+37
+00:01:21,000 --> 00:01:22,000
+I will just create that in demo.
+
+38
+00:01:22,000 --> 00:01:24,000
+I will say, hey, if someone wants
+
+39
+00:01:24,000 --> 00:01:28,000
+to try very advanced calculator, they can do that.
+
+40
+00:01:28,000 --> 00:01:30,000
+Okay? It is just that very advanced calculator.
+
+41
+00:01:30,000 --> 00:01:33,000
+If you can see, we don't have any of the methods. Okay?
+
+42
+00:01:33,000 --> 00:01:36,000
+Now that's an issue right?
+
+43
+00:01:36,000 --> 00:01:38,000
+Now I know in your mind you have a solution, right?
+
+44
+00:01:38,000 --> 00:01:40,000
+You have a choice. You can just add,
+
+45
+00:01:40,000 --> 00:01:42,000
+you can just type all these methods here
+
+46
+00:01:42,000 --> 00:01:46,000
+or we can come back here and say extends.
+
+47
+00:01:46,000 --> 00:01:47,000
+Okay? Now it'll extends what?.
+
+48
+00:01:47,000 --> 00:01:49,000
+We can also say calculator,
+
+49
+00:01:49,000 --> 00:01:52,000
+but then this will only have addition, subtraction,
+
+50
+00:01:52,000 --> 00:01:53,000
+division, multiplication,
+
+51
+00:01:53,000 --> 00:01:55,000
+but not the feature of advanced calculator,
+
+52
+00:01:55,000 --> 00:01:57,000
+which is, oh, it'll not have this two as well,
+
+53
+00:01:57,000 --> 00:02:00,000
+because this two is there in advanced calculator,
+
+54
+00:02:00,000 --> 00:02:01,000
+it'll only have add and sub.
+
+55
+00:02:01,000 --> 00:02:04,000
+You can see multi and division not found.
+
+56
+00:02:04,000 --> 00:02:05,000
+In fact, you know, I should also have R3.
+
+57
+00:02:05,000 --> 00:02:09,000
+In fact, this should be of type double, double R5 equal
+
+58
+00:02:09,000 --> 00:02:14,000
+to OBJ.power by passing two values.
+
+59
+00:02:14,000 --> 00:02:16,000
+One is, let's say four (indistinct),
+
+60
+00:02:16,000 --> 00:02:19,000
+at least we know the output should be 16.
+
+61
+00:02:19,000 --> 00:02:22,000
+And I also want to print R5.
+
+62
+00:02:22,000 --> 00:02:24,000
+Oh, we are printing everything in one line. Great.
+
+63
+00:02:24,000 --> 00:02:26,000
+And you can see multi and division are not working.
+
+64
+00:02:26,000 --> 00:02:28,000
+So if you want to make it work,
+
+65
+00:02:28,000 --> 00:02:29,000
+you can't just extends calculator, you have
+
+66
+00:02:29,000 --> 00:02:32,000
+to extends advanced calculator.
+
+67
+00:02:32,000 --> 00:02:34,000
+So you can see we have multiple hierarchy here.
+
+68
+00:02:34,000 --> 00:02:35,000
+So very advanced calculator is
+
+69
+00:02:35,000 --> 00:02:37,000
+extending advanced calculator.
+
+70
+00:02:37,000 --> 00:02:39,000
+Advanced calculator is extending calculator.
+
+71
+00:02:39,000 --> 00:02:42,000
+So if you try to compile this code, let's say if this works,
+
+72
+00:02:42,000 --> 00:02:45,000
+compile and run, you can see it's working.
+
+73
+00:02:45,000 --> 00:02:48,000
+You got 16 at the end, you got 0.0
+
+74
+00:02:48,000 --> 00:02:51,000
+because we are returning a double value.
+
+75
+00:02:51,000 --> 00:02:53,000
+This works. So if you're trying to imagine this,
+
+76
+00:02:53,000 --> 00:02:57,000
+what we are doing is, so we have a calculator
+
+77
+00:02:57,000 --> 00:03:00,000
+and then advanced calculator is extending calculator.
+
+78
+00:03:00,000 --> 00:03:04,000
+And then we got very advanced calculator is extending
+
+79
+00:03:04,000 --> 00:03:05,000
+from advanced calculator.
+
+80
+00:03:05,000 --> 00:03:08,000
+Now, this is when you are saying multiple,
+
+81
+00:03:08,000 --> 00:03:10,000
+where we are doing inheritance, right?
+
+82
+00:03:10,000 --> 00:03:14,000
+So this is called multilevel inheritance.
+
+83
+00:03:14,000 --> 00:03:17,000
+So basically we have multilevel inheritance here
+
+84
+00:03:17,000 --> 00:03:18,000
+because we have multiple level,
+
+85
+00:03:18,000 --> 00:03:22,000
+but in the early example we were having a just two, right?
+
+86
+00:03:22,000 --> 00:03:23,000
+So we were having this two.
+
+87
+00:03:23,000 --> 00:03:26,000
+Now when you say only two classes, this is called,
+
+88
+00:03:27,000 --> 00:03:30,000
+single level inheritance,
+
+89
+00:03:30,000 --> 00:03:32,000
+and I know I became a doctor there,
+
+90
+00:03:32,000 --> 00:03:34,000
+but you got the point, right?
+
+91
+00:03:34,000 --> 00:03:35,000
+So if you have multiple layers,
+
+92
+00:03:35,000 --> 00:03:37,000
+that is multi-level inheritance.
+
+93
+00:03:37,000 --> 00:03:39,000
+And when you say single, that is single,
+
+94
+00:03:39,000 --> 00:03:40,000
+when you have only two classes.
+
+95
+00:03:40,000 --> 00:03:44,000
+Now the very advanced calculator here is taking the feature
+
+96
+00:03:44,000 --> 00:03:45,000
+from advanced calculator.
+
+97
+00:03:45,000 --> 00:03:47,000
+Advanced calculator is taking the feature from calculator.
+
+98
+00:03:47,000 --> 00:03:50,000
+So by default, all the calc. stuff will come to
+
+99
+00:03:50,000 --> 00:03:52,000
+very advanced and that is multi-level.
+

02 - Core Java/053 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/054 Multiple Inheritance_en.srt

@@ -0,0 +1,656 @@
+1
+00:00:00,000 --> 00:00:03,000
+(gentle piano music)
+
+2
+00:00:03,000 --> 00:00:04,000
+-: So in the last video we have talked
+
+3
+00:00:04,000 --> 00:00:06,000
+about what is single level inheritance,
+
+4
+00:00:06,000 --> 00:00:08,000
+and then we have talked about multi-level, right?
+
+5
+00:00:08,000 --> 00:00:09,000
+Now what is multi-level?
+
+6
+00:00:09,000 --> 00:00:11,000
+So when you have the class,
+
+7
+00:00:11,000 --> 00:00:13,000
+which is getting inherited by someone else
+
+8
+00:00:13,000 --> 00:00:15,000
+and then something else is getting inherited
+
+9
+00:00:15,000 --> 00:00:16,000
+by something else.
+
+10
+00:00:16,000 --> 00:00:18,000
+It is multi-level.
+
+11
+00:00:18,000 --> 00:00:21,000
+Now, can we have a different structure here?
+
+12
+00:00:21,000 --> 00:00:22,000
+Let's take one more example.
+
+13
+00:00:22,000 --> 00:00:26,000
+So if you say we have A, we have B and we have C.
+
+14
+00:00:26,000 --> 00:00:28,000
+Now this is multi-level, right?
+
+15
+00:00:28,000 --> 00:00:31,000
+And of course when you have A and B, that's it.
+
+16
+00:00:31,000 --> 00:00:33,000
+This is single level.
+
+17
+00:00:33,000 --> 00:00:37,000
+But what if you have A and B, and then you have C,
+
+18
+00:00:37,000 --> 00:00:41,000
+where your A is your parent.
+
+19
+00:00:41,000 --> 00:00:42,000
+In fact, in this situation as well,
+
+20
+00:00:42,000 --> 00:00:44,000
+if you try to expand this one.
+
+21
+00:00:44,000 --> 00:00:49,000
+Here as well, we have this A as a parent,
+
+22
+00:00:50,000 --> 00:00:53,000
+and then this B becomes a child.
+
+23
+00:00:53,000 --> 00:00:55,000
+Now, B becomes child for A,
+
+24
+00:00:55,000 --> 00:00:59,000
+but then B is also a parent for C, right?
+
+25
+00:00:59,000 --> 00:01:00,000
+So C becomes child here.
+
+26
+00:01:00,000 --> 00:01:04,000
+Now, in the same way, if we talk about this A, B, C here.
+
+27
+00:01:04,000 --> 00:01:06,000
+We are saying both are parent,
+
+28
+00:01:06,000 --> 00:01:10,000
+so we have A as parent and B as parent,
+
+29
+00:01:10,000 --> 00:01:14,000
+and then C becomes a child.
+
+30
+00:01:14,000 --> 00:01:17,000
+So C is from A and B, both.
+
+31
+00:01:17,000 --> 00:01:19,000
+Now is it possible in Java?
+
+32
+00:01:19,000 --> 00:01:20,000
+Let's try.
+
+33
+00:01:20,000 --> 00:01:22,000
+In fact, it is possible in other language like C++.
+
+34
+00:01:22,000 --> 00:01:24,000
+Let's try in Java.
+
+35
+00:01:24,000 --> 00:01:26,000
+What I will do is I will just go back to the same class,
+
+36
+00:01:26,000 --> 00:01:28,000
+okay, same file, demo.
+
+37
+00:01:28,000 --> 00:01:30,000
+And here let me get a class called A.
+
+38
+00:01:30,000 --> 00:01:32,000
+And of course A will have some methods.
+
+39
+00:01:32,000 --> 00:01:34,000
+This should be capital A
+
+40
+00:01:34,000 --> 00:01:38,000
+and then class B and class C.
+
+41
+00:01:38,000 --> 00:01:42,000
+Okay, we have this three classes here, okay?
+
+42
+00:01:42,000 --> 00:01:46,000
+And let's say, okay, let's try this first.
+
+43
+00:01:46,000 --> 00:01:51,000
+If B extends from A and C extends from B, okay, this works.
+
+44
+00:01:54,000 --> 00:01:56,000
+We can see there's no problem here,
+
+45
+00:01:56,000 --> 00:02:01,000
+but what if I want the C to extends from A and B both.
+
+46
+00:02:01,000 --> 00:02:04,000
+As you can see, this syntax is not working.
+
+47
+00:02:04,000 --> 00:02:05,000
+It gives you an error as well.
+
+48
+00:02:05,000 --> 00:02:09,000
+You can't put a comma when you say extends A comma B, okay?
+
+49
+00:02:09,000 --> 00:02:12,000
+Does it means we can use extend B?
+
+50
+00:02:12,000 --> 00:02:13,000
+No, even this will not work.
+
+51
+00:02:13,000 --> 00:02:16,000
+So it doesn't matter what combination you do,
+
+52
+00:02:16,000 --> 00:02:20,000
+multiple inheritance in Java will not work.
+
+53
+00:02:20,000 --> 00:02:20,000
+Yeah.
+
+54
+00:02:20,000 --> 00:02:21,000
+So this thing will not work.
+
+55
+00:02:21,000 --> 00:02:24,000
+Multiple inheritance will not work.
+
+56
+00:02:24,000 --> 00:02:25,000
+But the question is why?
+
+57
+00:02:25,000 --> 00:02:27,000
+So let's try to understand that here.
+
+58
+00:02:27,000 --> 00:02:28,000
+Now, let's say if we go back
+
+59
+00:02:28,000 --> 00:02:30,000
+to this particular example here,
+
+60
+00:02:30,000 --> 00:02:33,000
+let's say you create object of B, okay?
+
+61
+00:02:33,000 --> 00:02:36,000
+In this scenario, if you create object of B, let's say obj.
+
+62
+00:02:36,000 --> 00:02:41,000
+Now, obj can call all the methods of B and A both.
+
+63
+00:02:41,000 --> 00:02:43,000
+So let's say in B, we have a method called show.
+
+64
+00:02:43,000 --> 00:02:45,000
+Okay, let's say there's a show method,
+
+65
+00:02:45,000 --> 00:02:49,000
+and then from obj, you are trying to call show.
+
+66
+00:02:49,000 --> 00:02:50,000
+Will this work?
+
+67
+00:02:50,000 --> 00:02:51,000
+Yes, this will work.
+
+68
+00:02:51,000 --> 00:02:55,000
+Let's say in A, we have a method called abc.
+
+69
+00:02:55,000 --> 00:02:59,000
+Now, if you try to call obj.abc, yes, this will work,
+
+70
+00:02:59,000 --> 00:03:02,000
+but what happens, you know when you say obj.abc,
+
+71
+00:03:02,000 --> 00:03:06,000
+it'll try to search for it first in the B class.
+
+72
+00:03:06,000 --> 00:03:07,000
+In B class, we don't have it.
+
+73
+00:03:07,000 --> 00:03:09,000
+So it'll say, okay, I don't have that method.
+
+74
+00:03:09,000 --> 00:03:11,000
+Maybe my parent class will have,
+
+75
+00:03:11,000 --> 00:03:13,000
+so it'll go to A by checking,
+
+76
+00:03:13,000 --> 00:03:14,000
+"Hey, do you have abc?"
+
+77
+00:03:14,000 --> 00:03:16,000
+Parent will say, "Yes, I have."
+
+78
+00:03:16,000 --> 00:03:18,000
+Now, in this case it'll work.
+
+79
+00:03:18,000 --> 00:03:20,000
+The same thing is applicable for C as well.
+
+80
+00:03:20,000 --> 00:03:23,000
+Let's say if you create object of C, which is obj again.
+
+81
+00:03:23,000 --> 00:03:26,000
+And then if you try to call a method,
+
+82
+00:03:26,000 --> 00:03:28,000
+let's say, A has a method called x,
+
+83
+00:03:28,000 --> 00:03:31,000
+B has a method called y and C has a method called z.
+
+84
+00:03:31,000 --> 00:03:33,000
+So let's say we have z method.
+
+85
+00:03:33,000 --> 00:03:35,000
+and then when you try to call z, this will work.
+
+86
+00:03:35,000 --> 00:03:37,000
+Because in C itself, we have the method.
+
+87
+00:03:37,000 --> 00:03:42,000
+If you say obj.y, will this work?
+
+88
+00:03:42,000 --> 00:03:44,000
+Yes, because it is coming from B.
+
+89
+00:03:44,000 --> 00:03:47,000
+Now, when you say obj.x,
+
+90
+00:03:47,000 --> 00:03:50,000
+it'll also work because it'll call from A.
+
+91
+00:03:50,000 --> 00:03:51,000
+So first it'll search in C.
+
+92
+00:03:51,000 --> 00:03:53,000
+In C, we don't have x, it'll go to B.
+
+93
+00:03:53,000 --> 00:03:55,000
+In B, also we don't have x.
+
+94
+00:03:55,000 --> 00:03:58,000
+It'll go to A, yes in A, we have x.
+
+95
+00:03:58,000 --> 00:04:00,000
+Okay, it works.
+
+96
+00:04:00,000 --> 00:04:02,000
+But now if you come back to this example,
+
+97
+00:04:02,000 --> 00:04:04,000
+let's say if you get object of C as obj.
+
+98
+00:04:04,000 --> 00:04:07,000
+So let's say this is C object, okay?
+
+99
+00:04:07,000 --> 00:04:10,000
+And then let's say in this A,
+
+100
+00:04:10,000 --> 00:04:12,000
+we have a method called show, okay?
+
+101
+00:04:12,000 --> 00:04:14,000
+And that's how we're working.
+
+102
+00:04:14,000 --> 00:04:17,000
+So let's say if you call show now,
+
+103
+00:04:17,000 --> 00:04:20,000
+now of course C will say, "Okay, I don't have a method show.
+
+104
+00:04:20,000 --> 00:04:22,000
+Will this work? Let me ask my parent."
+
+105
+00:04:22,000 --> 00:04:23,000
+So it'll go to A,
+
+106
+00:04:23,000 --> 00:04:26,000
+A will say, "Okay, I have show, problem solved."
+
+107
+00:04:26,000 --> 00:04:27,000
+This will work, right?
+
+108
+00:04:27,000 --> 00:04:28,000
+In general, I'm not talking about Java.
+
+109
+00:04:28,000 --> 00:04:30,000
+Let's say in general, this is how it works.
+
+110
+00:04:30,000 --> 00:04:34,000
+Now, let's say we have, in B, we have a method called X.
+
+111
+00:04:34,000 --> 00:04:35,000
+Okay?
+
+112
+00:04:35,000 --> 00:04:38,000
+Now it'll say obj.x, will this work?
+
+113
+00:04:38,000 --> 00:04:39,000
+Now it'll search and C.
+
+114
+00:04:39,000 --> 00:04:40,000
+In C, we don't have it.
+
+115
+00:04:40,000 --> 00:04:42,000
+In A, also we don't have it, in B we have it.
+
+116
+00:04:42,000 --> 00:04:44,000
+So this will also work.
+
+117
+00:04:44,000 --> 00:04:47,000
+Okay, but what if there's a method called y,
+
+118
+00:04:47,000 --> 00:04:51,000
+which is there in A and B, both, okay?
+
+119
+00:04:51,000 --> 00:04:55,000
+And now, if you're trying to say obj.y,
+
+120
+00:04:55,000 --> 00:04:59,000
+the problem is from C, we don't have it,
+
+121
+00:04:59,000 --> 00:05:03,000
+and A and B both has this method, which one he will choose?
+
+122
+00:05:03,000 --> 00:05:05,000
+That's a confusion, right?
+
+123
+00:05:05,000 --> 00:05:07,000
+It is almost same like let's say if you want
+
+124
+00:05:07,000 --> 00:05:09,000
+to call someone, your phone is dead,
+
+125
+00:05:09,000 --> 00:05:11,000
+and then now you want to call.
+
+126
+00:05:11,000 --> 00:05:12,000
+So you can ask your parents.
+
+127
+00:05:12,000 --> 00:05:13,000
+And both the parents has a phone,
+
+128
+00:05:13,000 --> 00:05:15,000
+which phone you will choose?
+
+129
+00:05:15,000 --> 00:05:18,000
+Now, if you chose your dad's phone,
+
+130
+00:05:18,000 --> 00:05:19,000
+your mom will feel bad.
+
+131
+00:05:19,000 --> 00:05:22,000
+If you choose your mom's phone, your dad will feel bad.
+
+132
+00:05:22,000 --> 00:05:25,000
+Again, I'm just giving an example here.
+
+133
+00:05:25,000 --> 00:05:26,000
+I'm not saying, it's literally happens,
+
+134
+00:05:26,000 --> 00:05:27,000
+but, in fact,
+
+135
+00:05:27,000 --> 00:05:29,000
+they'll be happy that you're not using their phone.
+
+136
+00:05:29,000 --> 00:05:32,000
+But yeah, that's a confusion we have here right now.
+
+137
+00:05:32,000 --> 00:05:36,000
+This problem is called ambiguity problem.
+
+138
+00:05:36,000 --> 00:05:37,000
+Okay?
+
+139
+00:05:37,000 --> 00:05:38,000
+So ambiguity simply means,
+
+140
+00:05:38,000 --> 00:05:40,000
+we have a confusion here, which one to choose?
+
+141
+00:05:40,000 --> 00:05:42,000
+Now, this problem is there in multiple languages,
+
+142
+00:05:42,000 --> 00:05:44,000
+which supports multiple inheritance.
+
+143
+00:05:44,000 --> 00:05:47,000
+Java says, "Oh, that's a problem?"
+
+144
+00:05:47,000 --> 00:05:49,000
+Let's remove the future itself.
+
+145
+00:05:49,000 --> 00:05:50,000
+Okay? I know.
+
+146
+00:05:50,000 --> 00:05:52,000
+That's a weird way of solving the problem,
+
+147
+00:05:52,000 --> 00:05:55,000
+but yeah, they have removed the problem itself.
+
+148
+00:05:55,000 --> 00:05:57,000
+So it's not like they found a solution.
+
+149
+00:05:57,000 --> 00:05:58,000
+They said,
+
+150
+00:05:58,000 --> 00:06:00,000
+"Instead of finding a solution, let's remove the feature."
+
+151
+00:06:00,000 --> 00:06:05,000
+That's right, in Java, multiple inheritance does not work.
+
+152
+00:06:05,000 --> 00:06:08,000
+Okay, so it's a very famous interview question,
+
+153
+00:06:08,000 --> 00:06:10,000
+do we support multiple inheritance in Java?
+
+154
+00:06:10,000 --> 00:06:11,000
+And the answer is no.
+
+155
+00:06:11,000 --> 00:06:13,000
+There is a internet way,
+
+156
+00:06:13,000 --> 00:06:15,000
+not actually a way,
+
+157
+00:06:15,000 --> 00:06:18,000
+just that it is possible by going all through steps.
+
+158
+00:06:18,000 --> 00:06:21,000
+But yeah, that's how Java is implemented in new feed,
+
+159
+00:06:21,000 --> 00:06:25,000
+in new versions, they have done something which changes it,
+
+160
+00:06:25,000 --> 00:06:26,000
+with the help of interfaces
+
+161
+00:06:26,000 --> 00:06:27,000
+but we don't know interfaces yet.
+
+162
+00:06:27,000 --> 00:06:32,000
+So, let's say, Java does not support multiple inheritance.
+
+163
+00:06:33,000 --> 00:06:35,000
+Oh, okay, this makes sense.
+
+164
+00:06:35,000 --> 00:06:36,000
+See you in the next video.
+

02 - Core Java/054 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/055 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/055 This and super method_en.srt

@@ -0,0 +1,1204 @@
+1
+00:00:00,000 --> 00:00:03,000
+(soft music plays)
+
+2
+00:00:03,000 --> 00:00:06,000
+-: In this video, let's talk about this and super.
+
+3
+00:00:06,000 --> 00:00:09,000
+Now this is a very super concept, so let's focus, so
+
+4
+00:00:09,000 --> 00:00:10,000
+what I'll do is I'll just remove all this thing just
+
+5
+00:00:10,000 --> 00:00:13,000
+to make it simple and clear this part as well.
+
+6
+00:00:13,000 --> 00:00:18,000
+And for this, I don't even need this particular classes,
+
+7
+00:00:18,000 --> 00:00:21,000
+so let me just close these files and keep it simple.
+
+8
+00:00:21,000 --> 00:00:22,000
+Okay, so we have a very simple code here.
+
+9
+00:00:22,000 --> 00:00:25,000
+Now what I'll do is just to understand this
+
+10
+00:00:25,000 --> 00:00:28,000
+and Super, I will create a class called A,
+
+11
+00:00:28,000 --> 00:00:29,000
+I know this is a very simple name,
+
+12
+00:00:29,000 --> 00:00:32,000
+but just for the example we can take them
+
+13
+00:00:32,000 --> 00:00:34,000
+and then we got a class B.
+
+14
+00:00:34,000 --> 00:00:36,000
+Okay, we got two classes
+
+15
+00:00:36,000 --> 00:00:41,000
+and then I'm also saying that this B class extends A,
+
+16
+00:00:41,000 --> 00:00:44,000
+of course we are doing inheritance here and it makes sense
+
+17
+00:00:44,000 --> 00:00:46,000
+because we just talked about inheritance.
+
+18
+00:00:46,000 --> 00:00:48,000
+And then what I will do is I will create
+
+19
+00:00:48,000 --> 00:00:49,000
+a constructor for both.
+
+20
+00:00:49,000 --> 00:00:51,000
+Of course we can do that, right?
+
+21
+00:00:51,000 --> 00:00:53,000
+Now before creating a constructor,
+
+22
+00:00:53,000 --> 00:00:55,000
+let me say if I create object of B,
+
+23
+00:00:55,000 --> 00:00:57,000
+of course we can do that, right?
+
+24
+00:00:57,000 --> 00:01:00,000
+So this B class, we got an object of B class here
+
+25
+00:01:00,000 --> 00:01:01,000
+and we can do that.
+
+26
+00:01:01,000 --> 00:01:04,000
+Let me create a constructor of B here.
+
+27
+00:01:04,000 --> 00:01:06,000
+Now how do we create a constructor? It's very simple.
+
+28
+00:01:06,000 --> 00:01:09,000
+You specify public and then you say B, bracket open,
+
+29
+00:01:09,000 --> 00:01:13,000
+and then here I will type in B.
+
+30
+00:01:13,000 --> 00:01:14,000
+I'm just trying to keep it as simple as possible.
+
+31
+00:01:14,000 --> 00:01:16,000
+That's why we have taken class A and B
+
+32
+00:01:16,000 --> 00:01:18,000
+and then a very simple statement.
+
+33
+00:01:18,000 --> 00:01:20,000
+Now what I will do is I will try to compile this code
+
+34
+00:01:20,000 --> 00:01:22,000
+and you tell me what will be the output.
+
+35
+00:01:22,000 --> 00:01:23,000
+Compression done, right?
+
+36
+00:01:23,000 --> 00:01:26,000
+If I run this code, there will be some output. Right?
+
+37
+00:01:26,000 --> 00:01:28,000
+Now think about this: We are creating the object of B.
+
+38
+00:01:28,000 --> 00:01:32,000
+We are instantiating it and we have learned about this that
+
+39
+00:01:32,000 --> 00:01:33,000
+whenever you create the object,
+
+40
+00:01:33,000 --> 00:01:35,000
+it'll call the constructor of a class.
+
+41
+00:01:35,000 --> 00:01:37,000
+So the object we are getting is of B,
+
+42
+00:01:37,000 --> 00:01:40,000
+and we have a constructor, which is B here,
+
+43
+00:01:40,000 --> 00:01:42,000
+which prints a statement.
+
+44
+00:01:42,000 --> 00:01:43,000
+So of course I'm expecting
+
+45
+00:01:43,000 --> 00:01:46,000
+that it'll execute the constructor and it will.
+
+46
+00:01:46,000 --> 00:01:48,000
+That's what you got in B.
+
+47
+00:01:48,000 --> 00:01:49,000
+That perfectly makes sense and we have talked
+
+48
+00:01:49,000 --> 00:01:50,000
+about this from a long time.
+
+49
+00:01:50,000 --> 00:01:54,000
+The twist here is, what if I have a constructor
+
+50
+00:01:54,000 --> 00:01:56,000
+in A as well?
+
+51
+00:01:56,000 --> 00:01:59,000
+And here I'm printing in A.
+
+52
+00:01:59,000 --> 00:02:01,000
+Now what do you think will be the output?
+
+53
+00:02:01,000 --> 00:02:05,000
+Because of course we are grading the object of B, not A,
+
+54
+00:02:05,000 --> 00:02:09,000
+so it should call the constructor of B and that makes sense.
+
+55
+00:02:09,000 --> 00:02:10,000
+But if you compile this code,
+
+56
+00:02:10,000 --> 00:02:12,000
+you will see something strange.
+
+57
+00:02:12,000 --> 00:02:13,000
+If I compile this code
+
+58
+00:02:13,000 --> 00:02:17,000
+and run, oh, it is also executing the constructor of A.
+
+59
+00:02:17,000 --> 00:02:19,000
+Now that's weird for us, right?
+
+60
+00:02:19,000 --> 00:02:22,000
+Because we are creating object of B,
+
+61
+00:02:22,000 --> 00:02:24,000
+it should only call the construct of B,
+
+62
+00:02:24,000 --> 00:02:26,000
+but it is also calling the construct of A,
+
+63
+00:02:26,000 --> 00:02:28,000
+and that sounds weird.
+
+64
+00:02:28,000 --> 00:02:31,000
+Now we understand that, but at this point, just remember
+
+65
+00:02:31,000 --> 00:02:32,000
+whenever you get object of a class,
+
+66
+00:02:32,000 --> 00:02:36,000
+it'll call the constructor of subclass and superclass both.
+
+67
+00:02:36,000 --> 00:02:39,000
+A is a superclass here, B is subclass.
+
+68
+00:02:39,000 --> 00:02:41,000
+It'll call the constructor of both.
+
+69
+00:02:41,000 --> 00:02:43,000
+Why? We'll talk about it in some time,
+
+70
+00:02:43,000 --> 00:02:45,000
+but it calls the constructor of both.
+
+71
+00:02:45,000 --> 00:02:46,000
+Now let me just add a twist here,
+
+72
+00:02:46,000 --> 00:02:50,000
+in B, let me create a parameterize constructor,
+
+73
+00:02:50,000 --> 00:02:51,000
+and we have seen that, right?
+
+74
+00:02:51,000 --> 00:02:53,000
+So what is parameterize constructor?
+
+75
+00:02:53,000 --> 00:02:55,000
+A constructor which takes a value.
+
+76
+00:02:55,000 --> 00:02:56,000
+Let's say this is N, okay?
+
+77
+00:02:56,000 --> 00:03:00,000
+And here, I'll print "in B int"
+
+78
+00:03:00,000 --> 00:03:03,000
+because we have a constructor which takes
+
+79
+00:03:03,000 --> 00:03:04,000
+a int n parameter.
+
+80
+00:03:04,000 --> 00:03:07,000
+I'm just printing just int just to differentiate
+
+81
+00:03:07,000 --> 00:03:08,000
+between these two statements.
+
+82
+00:03:08,000 --> 00:03:11,000
+Now with this, if I compile this code and run,
+
+83
+00:03:11,000 --> 00:03:11,000
+what do you think?
+
+84
+00:03:11,000 --> 00:03:13,000
+What will be the output?
+
+85
+00:03:13,000 --> 00:03:14,000
+Compile and run.
+
+86
+00:03:14,000 --> 00:03:16,000
+Still it is in A and in B.
+
+87
+00:03:16,000 --> 00:03:18,000
+Why not in B int is because
+
+88
+00:03:18,000 --> 00:03:20,000
+when you are creating the object,
+
+89
+00:03:20,000 --> 00:03:22,000
+you are not passing any value here.
+
+90
+00:03:22,000 --> 00:03:25,000
+Basically you are calling a default constructor,
+
+91
+00:03:25,000 --> 00:03:27,000
+but if you pass a value, let's say five,
+
+92
+00:03:27,000 --> 00:03:30,000
+in this case you are specifically mentioning, "Hey,
+
+93
+00:03:30,000 --> 00:03:32,000
+I'm creating an object of B
+
+94
+00:03:32,000 --> 00:03:34,000
+and I'm passing a integer here,
+
+95
+00:03:34,000 --> 00:03:38,000
+so it'll call the constructor of B, which takes integer.
+
+96
+00:03:38,000 --> 00:03:41,000
+Now by doing this, if I run this code,
+
+97
+00:03:41,000 --> 00:03:43,000
+or you can see it is printing in A
+
+98
+00:03:43,000 --> 00:03:45,000
+and in B, int.
+
+99
+00:03:45,000 --> 00:03:47,000
+Okay, that actually makes sense.
+
+100
+00:03:47,000 --> 00:03:49,000
+It'll call the construct of A,
+
+101
+00:03:49,000 --> 00:03:53,000
+but what if I also have a parameterize constructor in
+
+102
+00:03:53,000 --> 00:03:55,000
+A as well, which takes a N
+
+103
+00:03:55,000 --> 00:03:59,000
+and it also prints in A int.
+
+104
+00:03:59,000 --> 00:04:02,000
+Now, since we were not having a parameterize constructor,
+
+105
+00:04:02,000 --> 00:04:03,000
+it was called a (indistinct) constructor.
+
+106
+00:04:03,000 --> 00:04:05,000
+That's what I'm assuming at this point.
+
+107
+00:04:05,000 --> 00:04:08,000
+Now, when you have a parameterize constructor for both,
+
+108
+00:04:08,000 --> 00:04:10,000
+for A and B both,
+
+109
+00:04:10,000 --> 00:04:12,000
+now there is an expectation
+
+110
+00:04:12,000 --> 00:04:15,000
+that it'll print in A int and in B int.
+
+111
+00:04:15,000 --> 00:04:16,000
+And that's what I'm thinking.
+
+112
+00:04:16,000 --> 00:04:18,000
+I'm not sure what you are thinking.
+
+113
+00:04:18,000 --> 00:04:20,000
+Let's try, let's see if this works.
+
+114
+00:04:20,000 --> 00:04:23,000
+Oh no, what is happening here?
+
+115
+00:04:23,000 --> 00:04:26,000
+It is calling the the parameters constructor of B.
+
+116
+00:04:26,000 --> 00:04:27,000
+That actually makes sense, but why?
+
+117
+00:04:27,000 --> 00:04:29,000
+The default construct of A,
+
+118
+00:04:29,000 --> 00:04:32,000
+it should have been called this one, right?
+
+119
+00:04:32,000 --> 00:04:34,000
+Let's understand why it is first of all,
+
+120
+00:04:34,000 --> 00:04:36,000
+calling the constructor of parent class.
+
+121
+00:04:36,000 --> 00:04:37,000
+Why in the first place?
+
+122
+00:04:37,000 --> 00:04:40,000
+The thing is, and remember this point,
+
+123
+00:04:40,000 --> 00:04:45,000
+every constructor in Java has a method which is there,
+
+124
+00:04:47,000 --> 00:04:49,000
+even if you don't mention, okay?
+
+125
+00:04:49,000 --> 00:04:52,000
+And that method is super.
+
+126
+00:04:52,000 --> 00:04:56,000
+Now this method is there, even if you don't mention,
+
+127
+00:04:56,000 --> 00:04:57,000
+you can imagine that's like a John Cena.
+
+128
+00:04:57,000 --> 00:04:59,000
+I don't know if you know the John Cena memes.
+
+129
+00:04:59,000 --> 00:05:02,000
+It's just that you can't see it. Okay?
+
+130
+00:05:02,000 --> 00:05:03,000
+So super is there. You can't see it.
+
+131
+00:05:03,000 --> 00:05:06,000
+Even if you don't mention super, it is there.
+
+132
+00:05:06,000 --> 00:05:08,000
+So by default, every constructor,
+
+133
+00:05:08,000 --> 00:05:11,000
+the first statement is super
+
+134
+00:05:11,000 --> 00:05:14,000
+and every constructor not just this one,
+
+135
+00:05:14,000 --> 00:05:16,000
+every constructor, here as well.
+
+136
+00:05:16,000 --> 00:05:17,000
+Super, okay?
+
+137
+00:05:17,000 --> 00:05:20,000
+So every constructor will have super.
+
+138
+00:05:20,000 --> 00:05:22,000
+Same goes for A as well.
+
+139
+00:05:22,000 --> 00:05:23,000
+It'll also have super
+
+140
+00:05:24,000 --> 00:05:26,000
+and super,
+
+141
+00:05:26,000 --> 00:05:27,000
+irrespective to which class it is.
+
+142
+00:05:27,000 --> 00:05:29,000
+It'll have this statement super,
+
+143
+00:05:29,000 --> 00:05:31,000
+even if you don't mention it, is there, okay?
+
+144
+00:05:31,000 --> 00:05:32,000
+That's a point to remember.
+
+145
+00:05:32,000 --> 00:05:35,000
+Now let's try to understand how it is working.
+
+146
+00:05:35,000 --> 00:05:36,000
+Let's do a dry run.
+
+147
+00:05:36,000 --> 00:05:39,000
+The moment you execute this statement, what is happening?
+
+148
+00:05:39,000 --> 00:05:43,000
+It is calling the constructor of B, which is parametrized.
+
+149
+00:05:43,000 --> 00:05:46,000
+So it is calling this program method.
+
+150
+00:05:46,000 --> 00:05:47,000
+So when you execute this method,
+
+151
+00:05:47,000 --> 00:05:52,000
+the first thing it sees is super, not the system.println
+
+152
+00:05:52,000 --> 00:05:54,000
+What it is saying is super. Now what is super?
+
+153
+00:05:54,000 --> 00:05:57,000
+Now super method simply means call the constructor
+
+154
+00:05:57,000 --> 00:05:59,000
+of a super class.
+
+155
+00:05:59,000 --> 00:06:00,000
+So let me repeat.
+
+156
+00:06:00,000 --> 00:06:05,000
+Super means: call the constructor of a super class.
+
+157
+00:06:05,000 --> 00:06:07,000
+Now what's the in super class?
+
+158
+00:06:07,000 --> 00:06:10,000
+This is a super class, it is calling the constructor
+
+159
+00:06:10,000 --> 00:06:12,000
+of a super class, but which one?
+
+160
+00:06:12,000 --> 00:06:14,000
+The parameterized one.
+
+161
+00:06:14,000 --> 00:06:18,000
+So the default one, if you can see we are saying default,
+
+162
+00:06:18,000 --> 00:06:20,000
+we are not passing any parameter here.
+
+163
+00:06:20,000 --> 00:06:24,000
+So it is calling this particular constructor
+
+164
+00:06:24,000 --> 00:06:27,000
+and that's why it's printing in A,
+
+165
+00:06:27,000 --> 00:06:29,000
+and that's why if you can see the output,
+
+166
+00:06:29,000 --> 00:06:30,000
+it is first printing in A,
+
+167
+00:06:30,000 --> 00:06:34,000
+and then once it executes the A constructor,
+
+168
+00:06:34,000 --> 00:06:37,000
+it'll execute the remaining part of B constructor,
+
+169
+00:06:37,000 --> 00:06:40,000
+which is this part, in B int.
+
+170
+00:06:40,000 --> 00:06:42,000
+And that's why we got in B int, okay?
+
+171
+00:06:42,000 --> 00:06:46,000
+That means, if I don't want to call this constructor,
+
+172
+00:06:46,000 --> 00:06:49,000
+if I want to call the parameterized one, we have
+
+173
+00:06:49,000 --> 00:06:51,000
+to do only one change, which is
+
+174
+00:06:51,000 --> 00:06:55,000
+what if in this super you pass a number?
+
+175
+00:06:55,000 --> 00:06:57,000
+So any is a value, right? It'll have a value,
+
+176
+00:06:57,000 --> 00:07:00,000
+the same value you are passing to this super.
+
+177
+00:07:00,000 --> 00:07:02,000
+Now what we are saying is, "Hey Java, I know
+
+178
+00:07:02,000 --> 00:07:05,000
+you are going to execute this super class constructor,
+
+179
+00:07:05,000 --> 00:07:06,000
+but I'm passing a parameter there."
+
+180
+00:07:06,000 --> 00:07:08,000
+So now this time you have to call
+
+181
+00:07:08,000 --> 00:07:10,000
+the parameterized constructor.
+
+182
+00:07:10,000 --> 00:07:13,000
+By doing those changes, let's compile and run.
+
+183
+00:07:13,000 --> 00:07:14,000
+Here we go.
+
+184
+00:07:14,000 --> 00:07:17,000
+It is printing in A int and in B int.
+
+185
+00:07:17,000 --> 00:07:20,000
+So super is a very handy tool. It's there already.
+
+186
+00:07:20,000 --> 00:07:21,000
+You don't have to mention that,
+
+187
+00:07:21,000 --> 00:07:23,000
+but if you want to make some changes, of course you will
+
+188
+00:07:23,000 --> 00:07:24,000
+but you have to mention.
+
+189
+00:07:24,000 --> 00:07:26,000
+So if you want to pass a parametrized constructor,
+
+190
+00:07:26,000 --> 00:07:30,000
+then explicitly you have to mention super.
+
+191
+00:07:30,000 --> 00:07:33,000
+I hope that made some sense. Okay?
+
+192
+00:07:33,000 --> 00:07:35,000
+Now what I want is, I want to call
+
+193
+00:07:35,000 --> 00:07:38,000
+the default constructor of B.
+
+194
+00:07:38,000 --> 00:07:40,000
+Okay? I'm not passing any parameter here.
+
+195
+00:07:40,000 --> 00:07:42,000
+I'm calling a object of B.
+
+196
+00:07:42,000 --> 00:07:46,000
+So of course if I execute this, if I compile and run,
+
+197
+00:07:46,000 --> 00:07:49,000
+you can see it's printing in A and in B.
+
+198
+00:07:49,000 --> 00:07:50,000
+Why?
+
+199
+00:07:50,000 --> 00:07:52,000
+It's because when you are calling
+
+200
+00:07:52,000 --> 00:07:55,000
+the default constructor here in default construct of B,
+
+201
+00:07:55,000 --> 00:07:56,000
+it'll execute first.
+
+202
+00:07:56,000 --> 00:07:58,000
+It is calling this super,
+
+203
+00:07:58,000 --> 00:08:00,000
+that means it is calling this part constructor,
+
+204
+00:08:00,000 --> 00:08:05,000
+which is printing in A, and then it is printing in B.
+
+205
+00:08:05,000 --> 00:08:08,000
+It'll continue with this execution of B, right?
+
+206
+00:08:08,000 --> 00:08:11,000
+But what I want now is I know you got the point,
+
+207
+00:08:11,000 --> 00:08:14,000
+what I want is I want to execute in A int
+
+208
+00:08:14,000 --> 00:08:18,000
+and then I want to print in B.
+
+209
+00:08:18,000 --> 00:08:21,000
+So the output which I want is, in A INT in B.
+
+210
+00:08:21,000 --> 00:08:23,000
+So how can we play with that?
+
+211
+00:08:23,000 --> 00:08:26,000
+So what if here, if I pass a value at say five
+
+212
+00:08:26,000 --> 00:08:27,000
+or any number, doesn't matter.
+
+213
+00:08:27,000 --> 00:08:30,000
+If I pass a number, it'll try to create object of B
+
+214
+00:08:30,000 --> 00:08:31,000
+with a default constructor,
+
+215
+00:08:31,000 --> 00:08:33,000
+it'll execute a default constructor.
+
+216
+00:08:33,000 --> 00:08:36,000
+But now we are calling a super class constructor
+
+217
+00:08:36,000 --> 00:08:38,000
+by passing a value.
+
+218
+00:08:38,000 --> 00:08:41,000
+So which constructor will be called?
+
+219
+00:08:41,000 --> 00:08:46,000
+Of course the second one and it'll print in A int in B.
+
+220
+00:08:46,000 --> 00:08:49,000
+Let's try, compile, run.
+
+221
+00:08:49,000 --> 00:08:50,000
+And that's what we got.
+
+222
+00:08:50,000 --> 00:08:54,000
+So that's how we can play with super and that is fun. Right?
+
+223
+00:08:54,000 --> 00:08:55,000
+Now I have a question for you.
+
+224
+00:08:55,000 --> 00:08:57,000
+Maybe you have observed it or not.
+
+225
+00:08:57,000 --> 00:08:59,000
+See in B class, when we are saying super,
+
+226
+00:08:59,000 --> 00:09:02,000
+it actually makes sense because we have a super class for B.
+
+227
+00:09:02,000 --> 00:09:05,000
+Okay? This is A here is a super class.
+
+228
+00:09:05,000 --> 00:09:08,000
+But when you say super for A, what is a super class for A?
+
+229
+00:09:08,000 --> 00:09:10,000
+We have not mentioned anything here, right?
+
+230
+00:09:10,000 --> 00:09:12,000
+Okay, now that's why we have to introduce
+
+231
+00:09:12,000 --> 00:09:13,000
+a new concept here.
+
+232
+00:09:13,000 --> 00:09:16,000
+Every class in Java, let me repeat.
+
+233
+00:09:16,000 --> 00:09:21,000
+Every class in Java extends the object class.
+
+234
+00:09:22,000 --> 00:09:27,000
+So object is a class in Java, which has a lot of methods.
+
+235
+00:09:27,000 --> 00:09:28,000
+We'll talk about those methods later.
+
+236
+00:09:28,000 --> 00:09:32,000
+But every class in Java extends this class.
+
+237
+00:09:32,000 --> 00:09:34,000
+Even if you don't mention, so even
+
+238
+00:09:34,000 --> 00:09:36,000
+if you don't mention this, it is extending it.
+
+239
+00:09:36,000 --> 00:09:39,000
+Again, you can imagine this as a John Cena,
+
+240
+00:09:39,000 --> 00:09:40,000
+it's there, you can't see it.
+
+241
+00:09:40,000 --> 00:09:43,000
+Okay? So even if you don't mention, or you mention,
+
+242
+00:09:43,000 --> 00:09:44,000
+it's the same thing.
+
+243
+00:09:44,000 --> 00:09:46,000
+So when you say super here,
+
+244
+00:09:46,000 --> 00:09:50,000
+you're basically calling a constructor of the object class.
+
+245
+00:09:50,000 --> 00:09:53,000
+Okay? In object class, also we have a constructor.
+
+246
+00:09:53,000 --> 00:09:56,000
+This is what you are calling, cool, right?
+
+247
+00:09:56,000 --> 00:09:58,000
+So even if you don't mention it, it's there.
+
+248
+00:09:58,000 --> 00:10:01,000
+Now you might be thinking the B class must be
+
+249
+00:10:01,000 --> 00:10:02,000
+extending A and object both?
+
+250
+00:10:02,000 --> 00:10:06,000
+No, B class extends A, A class extends objects.
+
+251
+00:10:06,000 --> 00:10:08,000
+So this is multi-level inheritance, okay?
+
+252
+00:10:08,000 --> 00:10:10,000
+There's no multiples till now, okay?
+
+253
+00:10:10,000 --> 00:10:13,000
+So yeah, that's how it works. We have object class.
+
+254
+00:10:13,000 --> 00:10:16,000
+So this super represents the constructor
+
+255
+00:10:16,000 --> 00:10:17,000
+of the object class.
+
+256
+00:10:17,000 --> 00:10:20,000
+So we have talked about super, but what is this?
+
+257
+00:10:20,000 --> 00:10:22,000
+Okay, now let me introduce this here.
+
+258
+00:10:22,000 --> 00:10:25,000
+The output, which I want now is, I want to execute
+
+259
+00:10:25,000 --> 00:10:28,000
+both the constructor of B.
+
+260
+00:10:28,000 --> 00:10:29,000
+Okay? So let me just keep it default now,
+
+261
+00:10:29,000 --> 00:10:30,000
+let me say super,
+
+262
+00:10:30,000 --> 00:10:33,000
+I want to execute both the constructor of B.
+
+263
+00:10:33,000 --> 00:10:35,000
+So I want only one object, okay?
+
+264
+00:10:35,000 --> 00:10:38,000
+With one object, can I execute both the constructor?
+
+265
+00:10:38,000 --> 00:10:40,000
+Of course I want to execute the constructor of A,
+
+266
+00:10:40,000 --> 00:10:44,000
+which is default, but I want to execute the constructor
+
+267
+00:10:44,000 --> 00:10:46,000
+of both B.
+
+268
+00:10:46,000 --> 00:10:50,000
+So what I'm saying is, I want in A, I want in B
+
+269
+00:10:50,000 --> 00:10:53,000
+and in B int, is it possible?
+
+270
+00:10:53,000 --> 00:10:55,000
+For that, what we can do is,
+
+271
+00:10:55,000 --> 00:10:57,000
+see we are creating the constructor.
+
+272
+00:10:57,000 --> 00:11:00,000
+Let me pass a value here, let me pass five.
+
+273
+00:11:00,000 --> 00:11:01,000
+So of course by doing that,
+
+274
+00:11:01,000 --> 00:11:03,000
+what we are doing is we are calling the constructor,
+
+275
+00:11:03,000 --> 00:11:06,000
+which is the parametized one, and we are calling super
+
+276
+00:11:06,000 --> 00:11:09,000
+and that's what's calling the super class constructor.
+
+277
+00:11:09,000 --> 00:11:11,000
+But then we have one more method called this.
+
+278
+00:11:11,000 --> 00:11:13,000
+We have talked about this keyword, right?
+
+279
+00:11:13,000 --> 00:11:15,000
+Now, what this will do is,
+
+280
+00:11:15,000 --> 00:11:18,000
+this will execute the construct of a same class.
+
+281
+00:11:18,000 --> 00:11:19,000
+Let me repeat:
+
+282
+00:11:19,000 --> 00:11:23,000
+This will execute the constructor of a same class,
+
+283
+00:11:23,000 --> 00:11:24,000
+which is this one.
+
+284
+00:11:24,000 --> 00:11:26,000
+We are not passing in a parameter.
+
+285
+00:11:26,000 --> 00:11:29,000
+So it'll call the construct of a same class.
+
+286
+00:11:29,000 --> 00:11:32,000
+And then this constructor is calling the construct
+
+287
+00:11:32,000 --> 00:11:32,000
+of a super class.
+
+288
+00:11:32,000 --> 00:11:36,000
+Let's try this works, compile, run.
+
+289
+00:11:36,000 --> 00:11:40,000
+And you can see that we got in A, in B, in B int.
+
+290
+00:11:40,000 --> 00:11:43,000
+I mean of course this will execute first, this method,
+
+291
+00:11:43,000 --> 00:11:46,000
+but this particular method B constructor is
+
+292
+00:11:46,000 --> 00:11:49,000
+executing this, which is the default constructor.
+
+293
+00:11:49,000 --> 00:11:52,000
+The default constructor executes the super which goes here,
+
+294
+00:11:52,000 --> 00:11:57,000
+it'll execute in A, it'll execute in B and then in B int.
+
+295
+00:11:57,000 --> 00:12:00,000
+So that's what is, which is this keyword
+
+296
+00:12:00,000 --> 00:12:02,000
+and also this method and super method.
+
+297
+00:12:02,000 --> 00:12:05,000
+So this method execute the construct of a same class,
+
+298
+00:12:05,000 --> 00:12:08,000
+super method executes the construct of a super class.
+
+299
+00:12:08,000 --> 00:12:09,000
+So yeah, that's it from this video.
+
+300
+00:12:09,000 --> 00:12:10,000
+I hope you enjoyed it.
+
+301
+00:12:10,000 --> 00:12:13,000
+Let's see what we can do in the next video.
+

02 - Core Java/056 Method Overriding_en.srt

@@ -0,0 +1,808 @@
+1
+00:00:00,000 --> 00:00:02,000
+(bright music)
+
+2
+00:00:03,000 --> 00:00:05,000
+-: So once we talked about inheritance
+
+3
+00:00:05,000 --> 00:00:07,000
+and method overloading as well, right?
+
+4
+00:00:07,000 --> 00:00:08,000
+We have talked about method overloading.
+
+5
+00:00:08,000 --> 00:00:09,000
+In this video,
+
+6
+00:00:09,000 --> 00:00:12,000
+let's talk about method overriding. That's right.
+
+7
+00:00:12,000 --> 00:00:14,000
+So we have two different method,
+
+8
+00:00:14,000 --> 00:00:16,000
+overloading and method overriding.
+
+9
+00:00:16,000 --> 00:00:17,000
+So let's talk about overriding here.
+
+10
+00:00:17,000 --> 00:00:18,000
+So for that, what I will do is
+
+11
+00:00:18,000 --> 00:00:20,000
+I will just try to keep it simple again
+
+12
+00:00:20,000 --> 00:00:22,000
+and let's use the class A
+
+13
+00:00:22,000 --> 00:00:25,000
+and inside this class A, let's say we have a method.
+
+14
+00:00:25,000 --> 00:00:27,000
+So I will just remove this part.
+
+15
+00:00:27,000 --> 00:00:31,000
+And here I would say public void show.
+
+16
+00:00:31,000 --> 00:00:32,000
+Just to keep it simple,
+
+17
+00:00:32,000 --> 00:00:33,000
+I'm using a very simple example here,
+
+18
+00:00:33,000 --> 00:00:36,000
+which is show which prints something.
+
+19
+00:00:36,000 --> 00:00:39,000
+Let's say it prints in show, okay.
+
+20
+00:00:39,000 --> 00:00:42,000
+Now if you have a method inside a class,
+
+21
+00:00:42,000 --> 00:00:43,000
+of course you can create the object
+
+22
+00:00:43,000 --> 00:00:45,000
+and you can call the method, right,
+
+23
+00:00:45,000 --> 00:00:46,000
+and we have seen that.
+
+24
+00:00:46,000 --> 00:00:48,000
+So let's say if I go back to my main method,
+
+25
+00:00:48,000 --> 00:00:51,000
+if I say A obj = new A,
+
+26
+00:00:51,000 --> 00:00:56,000
+and I can simply say obj.show and it'll work, right.
+
+27
+00:00:56,000 --> 00:00:57,000
+And it should work.
+
+28
+00:00:57,000 --> 00:00:59,000
+That's what we have done from a long time.
+
+29
+00:00:59,000 --> 00:01:02,000
+So let's compile this code and run.
+
+30
+00:01:02,000 --> 00:01:04,000
+And you can see it prints in show.
+
+31
+00:01:04,000 --> 00:01:06,000
+Just to keep it simple, we have went
+
+32
+00:01:06,000 --> 00:01:08,000
+with a very simple example.
+
+33
+00:01:08,000 --> 00:01:09,000
+Now what I wanna do is
+
+34
+00:01:09,000 --> 00:01:12,000
+I want to get a class which is class B,
+
+35
+00:01:12,000 --> 00:01:15,000
+and I want this class B to extends class A.
+
+36
+00:01:15,000 --> 00:01:18,000
+And of course when you talk about inheritance,
+
+37
+00:01:18,000 --> 00:01:19,000
+this method of show,
+
+38
+00:01:19,000 --> 00:01:21,000
+it also will be available inside Class B, right.
+
+39
+00:01:21,000 --> 00:01:25,000
+So if I create object of class B instead of A,
+
+40
+00:01:25,000 --> 00:01:28,000
+it'll also work because that's how inheritance works, right.
+
+41
+00:01:28,000 --> 00:01:31,000
+So if I go back, compile and run, it works.
+
+42
+00:01:31,000 --> 00:01:33,000
+You can see we got in show.
+
+43
+00:01:33,000 --> 00:01:37,000
+What I do now is I will also print in A show
+
+44
+00:01:37,000 --> 00:01:40,000
+just to differentiate that this is getting printed
+
+45
+00:01:40,000 --> 00:01:41,000
+in the A class, okay.
+
+46
+00:01:41,000 --> 00:01:43,000
+Now the thing is,
+
+47
+00:01:43,000 --> 00:01:47,000
+what if you want to have a different definition of it?
+
+48
+00:01:47,000 --> 00:01:48,000
+Okay, why do we need different definition?
+
+49
+00:01:48,000 --> 00:01:52,000
+Let's say we got two methods here, public void config.
+
+50
+00:01:52,000 --> 00:01:54,000
+So let's say we have this method which is called config.
+
+51
+00:01:54,000 --> 00:01:55,000
+I don't know what it'll do.
+
+52
+00:01:55,000 --> 00:01:58,000
+Just to keep it simple, I will just say S out
+
+53
+00:01:58,000 --> 00:02:01,000
+and I will say this is in a config, okay.
+
+54
+00:02:01,000 --> 00:02:03,000
+And let's say they have different implementation,
+
+55
+00:02:03,000 --> 00:02:04,000
+they have different statements.
+
+56
+00:02:04,000 --> 00:02:06,000
+At this point, we are not focusing on statements.
+
+57
+00:02:06,000 --> 00:02:08,000
+We are here to understand the concept, right?
+
+58
+00:02:08,000 --> 00:02:10,000
+So let's say it does something,
+
+59
+00:02:10,000 --> 00:02:12,000
+so method and config does something
+
+60
+00:02:12,000 --> 00:02:15,000
+and I can actually call both the methods, not just one.
+
+61
+00:02:15,000 --> 00:02:17,000
+I can call config as well, okay?
+
+62
+00:02:17,000 --> 00:02:21,000
+And if I compile and run this code, it works.
+
+63
+00:02:21,000 --> 00:02:24,000
+You can see it says in A show in A config.
+
+64
+00:02:24,000 --> 00:02:28,000
+Now, let's say I want a different definition for show, okay,
+
+65
+00:02:28,000 --> 00:02:29,000
+not for config.
+
+66
+00:02:29,000 --> 00:02:32,000
+So basically what I want is when it comes to B,
+
+67
+00:02:32,000 --> 00:02:36,000
+and when I call show, it should print in B show.
+
+68
+00:02:36,000 --> 00:02:39,000
+How do I do that? How do I change the execution?
+
+69
+00:02:39,000 --> 00:02:41,000
+So what I want is when I call show,
+
+70
+00:02:41,000 --> 00:02:43,000
+it should not call the show of A
+
+71
+00:02:43,000 --> 00:02:46,000
+because show of A will print in A show.
+
+72
+00:02:46,000 --> 00:02:47,000
+I want to use config as it is.
+
+73
+00:02:47,000 --> 00:02:49,000
+So I can't even remove this inheritance.
+
+74
+00:02:49,000 --> 00:02:52,000
+If I remove this, and if I define the methods,
+
+75
+00:02:52,000 --> 00:02:53,000
+of course I can define show,
+
+76
+00:02:53,000 --> 00:02:57,000
+but then I want this config to be coming from A.
+
+77
+00:02:57,000 --> 00:02:58,000
+So of course you have to keep it.
+
+78
+00:02:58,000 --> 00:03:02,000
+You have to say Class B extends A, because we want config.
+
+79
+00:03:02,000 --> 00:03:05,000
+What we don't want of A is show
+
+80
+00:03:05,000 --> 00:03:07,000
+because it is printing in A show.
+
+81
+00:03:07,000 --> 00:03:08,000
+I wanna do something else.
+
+82
+00:03:08,000 --> 00:03:11,000
+In that scenario, you can say public void show,
+
+83
+00:03:11,000 --> 00:03:13,000
+you can write the same method name
+
+84
+00:03:13,000 --> 00:03:14,000
+or maybe a different name.
+
+85
+00:03:14,000 --> 00:03:17,000
+You can say in show1, I mean show1
+
+86
+00:03:17,000 --> 00:03:21,000
+and you can print here in B show.
+
+87
+00:03:21,000 --> 00:03:22,000
+I mean of course you can do this.
+
+88
+00:03:22,000 --> 00:03:24,000
+The only thing is
+
+89
+00:03:24,000 --> 00:03:26,000
+if you execute this code now,
+
+90
+00:03:26,000 --> 00:03:28,000
+it'll still print in A show.
+
+91
+00:03:28,000 --> 00:03:30,000
+You know why? is because we are calling show,
+
+92
+00:03:30,000 --> 00:03:32,000
+and both these methods are different.
+
+93
+00:03:32,000 --> 00:03:36,000
+One with name show and one with name show1, okay.
+
+94
+00:03:36,000 --> 00:03:37,000
+That means if I call show1, then it'll work,
+
+95
+00:03:37,000 --> 00:03:40,000
+then it'll print in B show.
+
+96
+00:03:40,000 --> 00:03:41,000
+But what I want is
+
+97
+00:03:41,000 --> 00:03:43,000
+I want them to have a same name.
+
+98
+00:03:43,000 --> 00:03:46,000
+I want my this method, which is show
+
+99
+00:03:46,000 --> 00:03:49,000
+should override the method here.
+
+100
+00:03:49,000 --> 00:03:50,000
+Is it possible?
+
+101
+00:03:50,000 --> 00:03:51,000
+And the answer is yes.
+
+102
+00:03:51,000 --> 00:03:53,000
+In Java we get this amazing feature where
+
+103
+00:03:53,000 --> 00:03:56,000
+you can basically override the methods
+
+104
+00:03:56,000 --> 00:03:57,000
+of the patent class.
+
+105
+00:03:57,000 --> 00:04:02,000
+So of course you want everything except this part. Okay.
+
+106
+00:04:02,000 --> 00:04:03,000
+I mean, except this show method.
+
+107
+00:04:03,000 --> 00:04:05,000
+I want config, but I don't want show.
+
+108
+00:04:05,000 --> 00:04:06,000
+Now, let me give you one more example here.
+
+109
+00:04:06,000 --> 00:04:08,000
+Remember when we talked about inheritance,
+
+110
+00:04:08,000 --> 00:04:09,000
+I have used an example
+
+111
+00:04:09,000 --> 00:04:12,000
+where I was not having any phone in my 10 standard
+
+112
+00:04:12,000 --> 00:04:15,000
+and my father had a phone, which is 3310.
+
+113
+00:04:15,000 --> 00:04:18,000
+Now if you ask me at that point, which phone I have,
+
+114
+00:04:18,000 --> 00:04:22,000
+I would just say 3310 because that's my father's phone.
+
+115
+00:04:22,000 --> 00:04:24,000
+But after two years, when I was in my 12 standard,
+
+116
+00:04:24,000 --> 00:04:25,000
+I got my own phone.
+
+117
+00:04:25,000 --> 00:04:27,000
+I got Motorola C168.
+
+118
+00:04:27,000 --> 00:04:29,000
+Again, not a smart phone,
+
+119
+00:04:29,000 --> 00:04:32,000
+but it was good, it was a very slim phone.
+
+120
+00:04:32,000 --> 00:04:35,000
+So when now if you ask me which phone I have,
+
+121
+00:04:35,000 --> 00:04:37,000
+I will say I have Motorola C168.
+
+122
+00:04:37,000 --> 00:04:40,000
+My father still had 3310.
+
+123
+00:04:40,000 --> 00:04:41,000
+So here, if you can see,
+
+124
+00:04:41,000 --> 00:04:43,000
+if someone ask my father,
+
+125
+00:04:43,000 --> 00:04:45,000
+father will say, I have 3310.
+
+126
+00:04:45,000 --> 00:04:48,000
+If you ask me, I have a choice of saying 3310,
+
+127
+00:04:48,000 --> 00:04:52,000
+but I will go for C168, which is my phone, right?
+
+128
+00:04:52,000 --> 00:04:55,000
+So you always give preference to your own features first.
+
+129
+00:04:55,000 --> 00:04:58,000
+Example, if you call show here,
+
+130
+00:04:58,000 --> 00:04:59,000
+it'll execute the method of B
+
+131
+00:04:59,000 --> 00:05:01,000
+instead of executing the method of A.
+
+132
+00:05:01,000 --> 00:05:04,000
+So basically this method show
+
+133
+00:05:04,000 --> 00:05:07,000
+overrides the method of A here.
+
+134
+00:05:07,000 --> 00:05:10,000
+And we can simply execute, compile, and run.
+
+135
+00:05:10,000 --> 00:05:12,000
+You can see it prints in B show.
+
+136
+00:05:12,000 --> 00:05:13,000
+Now this will make much more sense
+
+137
+00:05:13,000 --> 00:05:16,000
+when we say we are creating not A,
+
+138
+00:05:16,000 --> 00:05:18,000
+but we are creating a calculator
+
+139
+00:05:18,000 --> 00:05:20,000
+which has a method called let's say,
+
+140
+00:05:20,000 --> 00:05:22,000
+let me remove config for some time.
+
+141
+00:05:22,000 --> 00:05:25,000
+Let's say that we have a method called add,
+
+142
+00:05:25,000 --> 00:05:28,000
+and this will return a value, okay.
+
+143
+00:05:28,000 --> 00:05:30,000
+And here, instead of printing this,
+
+144
+00:05:30,000 --> 00:05:31,000
+I can simply accept two values.
+
+145
+00:05:31,000 --> 00:05:35,000
+I can say int n1, int n2,
+
+146
+00:05:35,000 --> 00:05:37,000
+and here we have done this before
+
+147
+00:05:37,000 --> 00:05:38,000
+and that's why I'm writing this code very fast.
+
+148
+00:05:38,000 --> 00:05:43,000
+I can say return and n1+n2. Okay.
+
+149
+00:05:43,000 --> 00:05:46,000
+So if your class, which is instead of saying B,
+
+150
+00:05:46,000 --> 00:05:50,000
+I can say Advanced Calc, which is extending calc.
+
+151
+00:05:50,000 --> 00:05:52,000
+It'll also have some features.
+
+152
+00:05:52,000 --> 00:05:56,000
+But let's say I want to add two numbers,
+
+153
+00:05:56,000 --> 00:05:57,000
+which will also take int
+
+154
+00:05:57,000 --> 00:05:59,000
+and it'll have the same parameter, okay,
+
+155
+00:05:59,000 --> 00:06:01,000
+because in method overloading we have seen
+
+156
+00:06:01,000 --> 00:06:03,000
+it can have the same method name
+
+157
+00:06:03,000 --> 00:06:04,000
+but different parameters.
+
+158
+00:06:04,000 --> 00:06:06,000
+Here in method overriding,
+
+159
+00:06:06,000 --> 00:06:08,000
+it'll be same name, same parameters as well.
+
+160
+00:06:08,000 --> 00:06:10,000
+I mean same type of parameters,
+
+161
+00:06:10,000 --> 00:06:12,000
+not the name, doesn't matter name,
+
+162
+00:06:12,000 --> 00:06:13,000
+let's say n1, n2
+
+163
+00:06:13,000 --> 00:06:16,000
+and it'll have the same name, same number of parameters,
+
+164
+00:06:16,000 --> 00:06:18,000
+same type of parameters,
+
+165
+00:06:18,000 --> 00:06:19,000
+but it'll have a different behavior.
+
+166
+00:06:19,000 --> 00:06:20,000
+Let's say n1+n2+1.
+
+167
+00:06:20,000 --> 00:06:22,000
+I'm just adding extra one there.
+
+168
+00:06:22,000 --> 00:06:27,000
+So what I want is if I comment this section, okay,
+
+169
+00:06:27,000 --> 00:06:28,000
+at this point I'm not overriding it,
+
+170
+00:06:28,000 --> 00:06:31,000
+I just have add method inside calc,
+
+171
+00:06:31,000 --> 00:06:34,000
+and if I create the object of advanced calculator
+
+172
+00:06:34,000 --> 00:06:38,000
+by saying Advanced Calculator obj = new Advanced Calculator,
+
+173
+00:06:38,000 --> 00:06:42,000
+and if I try to call the add method by passing 3 and 4,
+
+174
+00:06:42,000 --> 00:06:44,000
+of course 3 and 4 is 7.
+
+175
+00:06:44,000 --> 00:06:46,000
+So if I get this value somewhere,
+
+176
+00:06:46,000 --> 00:06:48,000
+if I say int r1 =,
+
+177
+00:06:48,000 --> 00:06:51,000
+and if I print the value for r1,
+
+178
+00:06:51,000 --> 00:06:53,000
+and again, since we have done this code before,
+
+179
+00:06:53,000 --> 00:06:55,000
+I'm just typing it fast.
+
+180
+00:06:55,000 --> 00:06:57,000
+Now, what do you think? What will the output?
+
+181
+00:06:57,000 --> 00:06:58,000
+I'm passing 3 and 4.
+
+182
+00:06:58,000 --> 00:07:01,000
+So of course it'll first search for this method add
+
+183
+00:07:01,000 --> 00:07:03,000
+inside the same class.
+
+184
+00:07:03,000 --> 00:07:05,000
+Of course, we don't have that method.
+
+185
+00:07:05,000 --> 00:07:07,000
+So it'll go to the upper class by saying,
+
+186
+00:07:07,000 --> 00:07:10,000
+Hey, you know calc, you are my parent class,
+
+187
+00:07:10,000 --> 00:07:14,000
+I'm searching for add with you and yes, it is available.
+
+188
+00:07:14,000 --> 00:07:17,000
+So basically we can just compile this code and run.
+
+189
+00:07:17,000 --> 00:07:20,000
+You can see we got 7 and that actually works.
+
+190
+00:07:20,000 --> 00:07:23,000
+But now I want a different definition for add,
+
+191
+00:07:23,000 --> 00:07:24,000
+I just want some changes.
+
+192
+00:07:24,000 --> 00:07:26,000
+Instead of adding those two numbers,
+
+193
+00:07:26,000 --> 00:07:29,000
+it should also add 1 at the end, okay.
+
+194
+00:07:29,000 --> 00:07:33,000
+So if I compile this code now and run, it'll print 8.
+
+195
+00:07:33,000 --> 00:07:37,000
+So this add is overriding the add method of calculator.
+
+196
+00:07:37,000 --> 00:07:40,000
+Okay, just remove this statement, that's extra.
+
+197
+00:07:40,000 --> 00:07:44,000
+So this concept is called method overriding.
+
+198
+00:07:44,000 --> 00:07:47,000
+So this method is overriding the method here.
+
+199
+00:07:48,000 --> 00:07:50,000
+I hope that makes sense.
+
+200
+00:07:50,000 --> 00:07:52,000
+So this is method overriding.
+
+201
+00:07:52,000 --> 00:07:54,000
+In fact, there is one more trick here,
+
+202
+00:07:54,000 --> 00:07:56,000
+which we'll discuss in the next video.
+

02 - Core Java/056 Source-code.url

@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL=https://github.com/navinreddy20/Javacode.git

02 - Core Java/057 Packages_en.srt

@@ -0,0 +1,1252 @@
+1
+00:00:00,000 --> 00:00:03,000
+(soft instrumental music)
+
+2
+00:00:03,000 --> 00:00:05,000
+-: In this video let's talk about packages.
+
+3
+00:00:05,000 --> 00:00:07,000
+The thing is, whenever you have a file,
+
+4
+00:00:07,000 --> 00:00:11,000
+it doesn't matter is it music files or documents or code,
+
+5
+00:00:11,000 --> 00:00:13,000
+we normally put them in a folder, right?
+
+6
+00:00:13,000 --> 00:00:16,000
+And then we create a folder structure as well.
+
+7
+00:00:16,000 --> 00:00:19,000
+In fact, I remember in my college days when we used
+
+8
+00:00:19,000 --> 00:00:20,000
+to store different songs
+
+9
+00:00:20,000 --> 00:00:22,000
+we used to create different folders.
+
+10
+00:00:22,000 --> 00:00:26,000
+Like we have a Songs folder, then inside that we have
+
+11
+00:00:26,000 --> 00:00:30,000
+Rock Songs, DJ Songs, Sad Songs, Romantic Songs.
+
+12
+00:00:30,000 --> 00:00:33,000
+And in fact in that as well, when you go to Sad Songs
+
+13
+00:00:33,000 --> 00:00:36,000
+we can have Normal Sad Songs, Ultimate Sad Songs.
+
+14
+00:00:36,000 --> 00:00:38,000
+Okay, now that's exaggeration, but we do that, right?
+
+15
+00:00:38,000 --> 00:00:39,000
+We create a structure there.
+
+16
+00:00:39,000 --> 00:00:42,000
+In the same way, when you talk about Java project
+
+17
+00:00:42,000 --> 00:00:44,000
+you will not be creating one or two files, right?
+
+18
+00:00:44,000 --> 00:00:46,000
+It will be having multiple files.
+
+19
+00:00:46,000 --> 00:00:48,000
+Sometimes your project can have
+
+20
+00:00:48,000 --> 00:00:51,000
+let's say 200 files, 300 files.
+
+21
+00:00:51,000 --> 00:00:52,000
+Okay, maybe most of the time
+
+22
+00:00:52,000 --> 00:00:54,000
+when you have a complex project.
+
+23
+00:00:54,000 --> 00:00:57,000
+Now, how will you put all these files in one folder?
+
+24
+00:00:57,000 --> 00:00:59,000
+You can actually, you can put everything in one folder.
+
+25
+00:00:59,000 --> 00:01:02,000
+Now, if you see our project structure here,
+
+26
+00:01:02,000 --> 00:01:04,000
+what we did is we have this folder called CODES.
+
+27
+00:01:04,000 --> 00:01:07,000
+And in this CODES we have all of the files.
+
+28
+00:01:07,000 --> 00:01:09,000
+In fact, we only have three files now,
+
+29
+00:01:09,000 --> 00:01:11,000
+but just imagine we have more files.
+
+30
+00:01:11,000 --> 00:01:13,000
+Imagine if we have 100 files.
+
+31
+00:01:13,000 --> 00:01:15,000
+It's okay to put them in one folder,
+
+32
+00:01:15,000 --> 00:01:18,000
+but it's always better if you can create a structure
+
+33
+00:01:18,000 --> 00:01:21,000
+where you can have few files in one folder
+
+34
+00:01:21,000 --> 00:01:23,000
+and few files in another folder.
+
+35
+00:01:23,000 --> 00:01:26,000
+And then you can have a folder inside a folder.
+
+36
+00:01:26,000 --> 00:01:27,000
+Now, normally this type of pattern
+
+37
+00:01:27,000 --> 00:01:29,000
+in Java is called packages.
+
+38
+00:01:29,000 --> 00:01:32,000
+Normally you store files in a package.
+
+39
+00:01:32,000 --> 00:01:35,000
+So, yeah, that's right, the folder is package here.
+
+40
+00:01:35,000 --> 00:01:38,000
+And of course one package can be a part of another package
+
+41
+00:01:38,000 --> 00:01:40,000
+the way you have folders inside a folder.
+
+42
+00:01:40,000 --> 00:01:42,000
+So, how do we do that here in Java?
+
+43
+00:01:42,000 --> 00:01:44,000
+So, just to make you understand,
+
+44
+00:01:44,000 --> 00:01:45,000
+let's say we have these two files,
+
+45
+00:01:45,000 --> 00:01:47,000
+AdvancedCalculator and Calculator.
+
+46
+00:01:47,000 --> 00:01:49,000
+Now, these two files are related, right?
+
+47
+00:01:49,000 --> 00:01:51,000
+They both work for the calculator,
+
+48
+00:01:51,000 --> 00:01:55,000
+so it is a good idea to put them in one folder.
+
+49
+00:01:55,000 --> 00:01:56,000
+Now, how will you do that?
+
+50
+00:01:56,000 --> 00:01:58,000
+You have an option here of creating a new folder.
+
+51
+00:01:58,000 --> 00:01:59,000
+That's one way.
+
+52
+00:01:59,000 --> 00:02:01,000
+Or you can, what you can do is you can just come back
+
+53
+00:02:01,000 --> 00:02:04,000
+on top of your class and say you can create a package.
+
+54
+00:02:04,000 --> 00:02:06,000
+So, the keyword which you use
+
+55
+00:02:06,000 --> 00:02:07,000
+to create a package is called package,
+
+56
+00:02:07,000 --> 00:02:10,000
+and you can put this class in that particular package.
+
+57
+00:02:10,000 --> 00:02:13,000
+Let's say the package name is tools, right?
+
+58
+00:02:13,000 --> 00:02:15,000
+So, of course you can create any package name,
+
+59
+00:02:15,000 --> 00:02:17,000
+but it should have an, it should make some sense.
+
+60
+00:02:17,000 --> 00:02:21,000
+So, you can see I'm saying that they are tools, okay?
+
+61
+00:02:21,000 --> 00:02:24,000
+And the thing is you can see we are getting an error.
+
+62
+00:02:24,000 --> 00:02:26,000
+It says that declared package tools
+
+63
+00:02:26,000 --> 00:02:29,000
+does not match the expected package.
+
+64
+00:02:29,000 --> 00:02:33,000
+The thing is you don't have Calc inside the package.
+
+65
+00:02:33,000 --> 00:02:35,000
+In fact, most of the IDs will give you an option
+
+66
+00:02:35,000 --> 00:02:39,000
+of directly, if I click on Quick Fix, yeah.
+
+67
+00:02:39,000 --> 00:02:40,000
+So, you can see most of the IDs,
+
+68
+00:02:40,000 --> 00:02:42,000
+doesn't matter which ID you're using,
+
+69
+00:02:42,000 --> 00:02:44,000
+in VS Code we have this option.
+
+70
+00:02:44,000 --> 00:02:46,000
+In most of the famous ID you will get this option
+
+71
+00:02:46,000 --> 00:02:50,000
+of doing something, some red symbol or something like that.
+
+72
+00:02:50,000 --> 00:02:52,000
+Here we have an option of Quick Fix.
+
+73
+00:02:52,000 --> 00:02:57,000
+If I click on that it says Move Calc.java to package tools.
+
+74
+00:02:57,000 --> 00:02:59,000
+Okay, that is a good idea.
+
+75
+00:02:59,000 --> 00:03:00,000
+We can click on this,
+
+76
+00:03:00,000 --> 00:03:04,000
+and you can see it created a folder called tools.
+
+77
+00:03:04,000 --> 00:03:07,000
+And now we can actually move this to tools as well.
+
+78
+00:03:07,000 --> 00:03:09,000
+The only thing is when you do that
+
+79
+00:03:09,000 --> 00:03:13,000
+and when you go to this particular class, okay,
+
+80
+00:03:13,000 --> 00:03:14,000
+it has already done the changes.
+
+81
+00:03:14,000 --> 00:03:16,000
+You can see I have not written this.
+
+82
+00:03:16,000 --> 00:03:19,000
+It is already there thanks to VS Code and the IDE,
+
+83
+00:03:20,000 --> 00:03:21,000
+so basically you get this here.
+
+84
+00:03:21,000 --> 00:03:23,000
+So, it's always a good idea
+
+85
+00:03:23,000 --> 00:03:25,000
+to put your classes in a package.
+
+86
+00:03:25,000 --> 00:03:28,000
+You can create a complex structure.
+
+87
+00:03:28,000 --> 00:03:31,000
+If you want you can create one more folder here.
+
+88
+00:03:31,000 --> 00:03:35,000
+Let's say we got a folder called database,
+
+89
+00:03:35,000 --> 00:03:37,000
+or maybe dbconnections or dbclasses,
+
+90
+00:03:37,000 --> 00:03:39,000
+or maybe you can just simply say db.
+
+91
+00:03:39,000 --> 00:03:41,000
+Now, this db will have all the database connections.
+
+92
+00:03:41,000 --> 00:03:44,000
+So, let's say if you want to create some files
+
+93
+00:03:44,000 --> 00:03:47,000
+which will connect with MySQL, Oracle or,
+
+94
+00:03:47,000 --> 00:03:48,000
+it does something with database,
+
+95
+00:03:48,000 --> 00:03:52,000
+so you can put all those classes in database folder, okay?
+
+96
+00:03:52,000 --> 00:03:55,000
+Now, that's how you create a project structure here, okay?
+
+97
+00:03:55,000 --> 00:03:57,000
+The only thing is if you want,
+
+98
+00:03:57,000 --> 00:03:58,000
+if you have this structure here.
+
+99
+00:03:58,000 --> 00:04:01,000
+Let's say if you have Calc and Demo, AdvancedCalc,
+
+100
+00:04:01,000 --> 00:04:03,000
+and if you can see both are in a package now.
+
+101
+00:04:03,000 --> 00:04:07,000
+The only problem we will face is if you go to Demo,
+
+102
+00:04:07,000 --> 00:04:10,000
+and you can see Demo is not a part of any package.
+
+103
+00:04:10,000 --> 00:04:13,000
+Normally you put the main class,
+
+104
+00:04:13,000 --> 00:04:16,000
+so the class which has a main method separately,
+
+105
+00:04:16,000 --> 00:04:17,000
+outside the package so that you can
+
+106
+00:04:17,000 --> 00:04:19,000
+easily access other classes.
+
+107
+00:04:19,000 --> 00:04:21,000
+Okay, when I say easily access other classes can I do that?
+
+108
+00:04:21,000 --> 00:04:24,000
+Can I create object of Calc here?
+
+109
+00:04:24,000 --> 00:04:26,000
+So, if I say Calc obj equal to new Calc,
+
+110
+00:04:26,000 --> 00:04:28,000
+which was working earlier,
+
+111
+00:04:28,000 --> 00:04:31,000
+if you remember our previous examples.
+
+112
+00:04:31,000 --> 00:04:32,000
+It's not working now.
+
+113
+00:04:32,000 --> 00:04:34,000
+You can see it says Calc cannot be resolved.
+
+114
+00:04:34,000 --> 00:04:35,000
+What's wrong?
+
+115
+00:04:35,000 --> 00:04:38,000
+The problem is Demo and Calc,
+
+116
+00:04:38,000 --> 00:04:40,000
+now they are in two different folders.
+
+117
+00:04:40,000 --> 00:04:42,000
+You can't directly access it.
+
+118
+00:04:42,000 --> 00:04:44,000
+Okay, so when I say you cannot directly access it
+
+119
+00:04:44,000 --> 00:04:46,000
+do we have an indirect way?
+
+120
+00:04:46,000 --> 00:04:48,000
+Yes, we have an indirect way.
+
+121
+00:04:48,000 --> 00:04:51,000
+So, what you can do is if you see this bubble
+
+122
+00:04:51,000 --> 00:04:53,000
+it says Import Calc, that's right.
+
+123
+00:04:53,000 --> 00:04:56,000
+If you want to use Calc in your particular class
+
+124
+00:04:56,000 --> 00:04:58,000
+you have to say import Calc.
+
+125
+00:04:58,000 --> 00:05:00,000
+But then Calc belong where?
+
+126
+00:05:00,000 --> 00:05:03,000
+Calc belongs to tools.Calc.
+
+127
+00:05:03,000 --> 00:05:05,000
+So, basically you have to mention the package name
+
+128
+00:05:05,000 --> 00:05:07,000
+and then you have to mention the class name,
+
+129
+00:05:07,000 --> 00:05:08,000
+whichever you want to import.
+
+130
+00:05:08,000 --> 00:05:10,000
+And now you can see there's no issue.
+
+131
+00:05:10,000 --> 00:05:12,000
+How about AdvancedCalculator?
+
+132
+00:05:12,000 --> 00:05:14,000
+If I want to use AdvancedCalculator,
+
+133
+00:05:14,000 --> 00:05:17,000
+obj1 is equal to new AdvancedCalculator.
+
+134
+00:05:17,000 --> 00:05:20,000
+Okay, now you cannot access this one, you know why?
+
+135
+00:05:20,000 --> 00:05:23,000
+It's because we have only imported Calc,
+
+136
+00:05:23,000 --> 00:05:25,000
+not AdvancedCalculator.
+
+137
+00:05:25,000 --> 00:05:26,000
+How will you import this?
+
+138
+00:05:26,000 --> 00:05:27,000
+You're right.
+
+139
+00:05:27,000 --> 00:05:30,000
+Just come back here and say import tools.AdvancedCalculator.
+
+140
+00:05:31,000 --> 00:05:33,000
+So, whichever class you want to use
+
+141
+00:05:33,000 --> 00:05:35,000
+you can just import them.
+
+142
+00:05:35,000 --> 00:05:38,000
+In fact, Java internally has a lot of classes.
+
+143
+00:05:38,000 --> 00:05:39,000
+Example, let's say one of the classes,
+
+144
+00:05:39,000 --> 00:05:42,000
+which we're going to see in future, which is let's say list.
+
+145
+00:05:42,000 --> 00:05:46,000
+Now, when we use list, which is inbuilt class,
+
+146
+00:05:46,000 --> 00:05:47,000
+or inbuilt interface, what is interface?
+
+147
+00:05:47,000 --> 00:05:48,000
+We'll talk about that later.
+
+148
+00:05:48,000 --> 00:05:50,000
+Or maybe at this point we can talk about
+
+149
+00:05:50,000 --> 00:05:53,000
+let's say ArrayList, which is a class.
+
+150
+00:05:53,000 --> 00:05:56,000
+When we use ArrayList and when you create object of it,
+
+151
+00:05:56,000 --> 00:05:59,000
+I will say list is equal to new ArrayList.
+
+152
+00:06:00,000 --> 00:06:01,000
+Now, the moment you do that
+
+153
+00:06:01,000 --> 00:06:03,000
+it will also come from a package.
+
+154
+00:06:03,000 --> 00:06:06,000
+You can see it is now given by the IDE,
+
+155
+00:06:06,000 --> 00:06:08,000
+it is auto-completing it.
+
+156
+00:06:08,000 --> 00:06:10,000
+But if I remove this line you can see
+
+157
+00:06:10,000 --> 00:06:10,000
+it will give you error.
+
+158
+00:06:10,000 --> 00:06:12,000
+It says ArrayList cannot be found.
+
+159
+00:06:12,000 --> 00:06:14,000
+So, we have to import this one as well,
+
+160
+00:06:14,000 --> 00:06:16,000
+and this belongs to a package.
+
+161
+00:06:16,000 --> 00:06:21,000
+Now, that package is import java.util.ArrayList.
+
+162
+00:06:22,000 --> 00:06:23,000
+This you have to import.
+
+163
+00:06:23,000 --> 00:06:26,000
+Now, you might be thinking why we have two dots here,
+
+164
+00:06:26,000 --> 00:06:28,000
+java.util, how it looks like.
+
+165
+00:06:28,000 --> 00:06:30,000
+So, basically we have a Java folder.
+
+166
+00:06:30,000 --> 00:06:33,000
+Inside Java folder we have a util folder.
+
+167
+00:06:33,000 --> 00:06:36,000
+So, it's the folder inside the folder,
+
+168
+00:06:36,000 --> 00:06:38,000
+and Java has multiple folders if you can see.
+
+169
+00:06:38,000 --> 00:06:41,000
+Java., we have applet folder,
+
+170
+00:06:41,000 --> 00:06:46,000
+we have awt folder, beans folder, lang folder, io folder,
+
+171
+00:06:46,000 --> 00:06:47,000
+and all those things.
+
+172
+00:06:47,000 --> 00:06:51,000
+So, in general whatever class you use in Java
+
+173
+00:06:51,000 --> 00:06:53,000
+belongs to a package.
+
+174
+00:06:53,000 --> 00:06:55,000
+Let me repeat, whichever class,
+
+175
+00:06:55,000 --> 00:06:59,000
+inbuilt class which you use in Java, belongs to a package.
+
+176
+00:06:59,000 --> 00:07:02,000
+Now you'll be saying okay, everything makes sense,
+
+177
+00:07:02,000 --> 00:07:05,000
+but don't you think String is also a class?
+
+178
+00:07:05,000 --> 00:07:09,000
+And one of our favorite class, which is System.
+
+179
+00:07:09,000 --> 00:07:11,000
+System is also a class, right?
+
+180
+00:07:11,000 --> 00:07:14,000
+So, when we are using System we have never imported it.
+
+181
+00:07:14,000 --> 00:07:16,000
+So, when I say System.out.println,
+
+182
+00:07:17,000 --> 00:07:19,000
+there was no need to import the package.
+
+183
+00:07:19,000 --> 00:07:21,000
+But does System belong to a package?
+
+184
+00:07:21,000 --> 00:07:22,000
+And the answer is yes.
+
+185
+00:07:22,000 --> 00:07:27,000
+If I go to System and if I go on top here, can you see that?
+
+186
+00:07:27,000 --> 00:07:28,000
+It says package.
+
+187
+00:07:28,000 --> 00:07:30,000
+So, this class, System class,
+
+188
+00:07:30,000 --> 00:07:32,000
+belongs to our package java.lang,
+
+189
+00:07:32,000 --> 00:07:33,000
+but we never imported it.
+
+190
+00:07:33,000 --> 00:07:37,000
+The thing is, by default every Java file will have
+
+191
+00:07:37,000 --> 00:07:40,000
+java.lang by default imported.
+
+192
+00:07:40,000 --> 00:07:42,000
+So, even if you don't mention that it's there.
+
+193
+00:07:42,000 --> 00:07:45,000
+This line is there even if you don't mention.
+
+194
+00:07:45,000 --> 00:07:48,000
+Now, the thing is it's actually this, not this line.
+
+195
+00:07:48,000 --> 00:07:52,000
+What is by default is this, java.lang.*.
+
+196
+00:07:52,000 --> 00:07:53,000
+Now, what is this star?
+
+197
+00:07:53,000 --> 00:07:56,000
+Now, in one particular folder if you have multiple files,
+
+198
+00:07:56,000 --> 00:08:00,000
+and if you want all the files you can simply say star
+
+199
+00:08:00,000 --> 00:08:01,000
+just like we have tools here.
+
+200
+00:08:01,000 --> 00:08:03,000
+In tools we only have two files,
+
+201
+00:08:03,000 --> 00:08:05,000
+and we are importing both.
+
+202
+00:08:05,000 --> 00:08:06,000
+So, can we just do that?
+
+203
+00:08:06,000 --> 00:08:07,000
+Yes, we can.
+
+204
+00:08:07,000 --> 00:08:10,000
+So, we can simply put a star here, our job is done.
+
+205
+00:08:10,000 --> 00:08:13,000
+And by doing that I also removed the list.
+
+206
+00:08:13,000 --> 00:08:15,000
+We don't even need that, you know that.
+
+207
+00:08:15,000 --> 00:08:17,000
+So, basically if you want to import all the files
+
+208
+00:08:17,000 --> 00:08:19,000
+you can say star, okay?
+
+209
+00:08:19,000 --> 00:08:22,000
+So, that's how you can create a package in Java.
+
+210
+00:08:22,000 --> 00:08:24,000
+As I mentioned, you can create a folder inside a folder.
+
+211
+00:08:24,000 --> 00:08:27,000
+Example, let's say if I have a folder called other,
+
+212
+00:08:27,000 --> 00:08:29,000
+so let's say we have other folder.
+
+213
+00:08:29,000 --> 00:08:32,000
+And this tools actually belongs to other,
+
+214
+00:08:32,000 --> 00:08:34,000
+so now if I move this you can see
+
+215
+00:08:34,000 --> 00:08:36,000
+we have tools inside other.
+
+216
+00:08:36,000 --> 00:08:40,000
+Now, how it will look like when you talk about your Calc,
+
+217
+00:08:40,000 --> 00:08:43,000
+so you can see it says other.Calc.
+
+218
+00:08:43,000 --> 00:08:45,000
+So, you have to, if you want to go inside the package,
+
+219
+00:08:45,000 --> 00:08:48,000
+normally in folder structure we use slash, here we use dot.
+
+220
+00:08:48,000 --> 00:08:52,000
+So, it is other.tools.Calc, okay?
+
+221
+00:08:52,000 --> 00:08:54,000
+That's how you have to import it.
+
+222
+00:08:54,000 --> 00:08:57,000
+And of course you can say star, it will import everything.
+
+223
+00:08:57,000 --> 00:09:01,000
+Now, my question to you is if I say import other.*,
+
+224
+00:09:02,000 --> 00:09:07,000
+now is these two line same or can I remove this?
+
+225
+00:09:07,000 --> 00:09:09,000
+Of course, when you say star it should import everything.
+
+226
+00:09:09,000 --> 00:09:12,000
+But no, if you can see, it is giving you error.
+
+227
+00:09:12,000 --> 00:09:15,000
+The reason is when you say other.* it,
+
+228
+00:09:15,000 --> 00:09:18,000
+so star simply means all the files
+
+229
+00:09:18,000 --> 00:09:20,000
+not all the folders, okay?
+
+230
+00:09:20,000 --> 00:09:22,000
+So, in other if you have some files,
+
+231
+00:09:22,000 --> 00:09:24,000
+let's say if I create a new file here.
+
+232
+00:09:24,000 --> 00:09:25,000
+I will name this as A.java.
+
+233
+00:09:25,000 --> 00:09:28,000
+The moment you do that you can see this A class
+
+234
+00:09:28,000 --> 00:09:29,000
+belongs to other package.
+
+235
+00:09:29,000 --> 00:09:32,000
+Now you can easily use A but not Calc.
+
+236
+00:09:32,000 --> 00:09:37,000
+So, if you say A obj2 is equal to new A, this will work.
+
+237
+00:09:37,000 --> 00:09:40,000
+It's because you are saying other.*,
+
+238
+00:09:40,000 --> 00:09:41,000
+it will import all the classes,
+
+239
+00:09:41,000 --> 00:09:44,000
+which are all the files in the other folder,
+
+240
+00:09:44,000 --> 00:09:46,000
+not inside the folder, which is tools.
+
+241
+00:09:46,000 --> 00:09:49,000
+So, if you want other, I mean tools as well,
+
+242
+00:09:49,000 --> 00:09:52,000
+so you have to mention other.tools.*.
+
+243
+00:09:53,000 --> 00:09:55,000
+So, that's how basically you use a package structure.
+
+244
+00:09:55,000 --> 00:09:57,000
+Now, there's one thing you know,
+
+245
+00:09:57,000 --> 00:09:58,000
+not important at this point,
+
+246
+00:09:58,000 --> 00:10:01,000
+but since we're talking about package let's talk about it
+
+247
+00:10:01,000 --> 00:10:02,000
+because you will be seeing
+
+248
+00:10:02,000 --> 00:10:04,000
+those type of structure multiple times.
+
+249
+00:10:04,000 --> 00:10:06,000
+When you create a project, a big project,
+
+250
+00:10:06,000 --> 00:10:08,000
+normally you deploy your project
+
+251
+00:10:08,000 --> 00:10:10,000
+on the server somewhere, right?
+
+252
+00:10:10,000 --> 00:10:12,000
+And maybe you're creating a library, that's right.
+
+253
+00:10:12,000 --> 00:10:14,000
+What you do is when you create a project
+
+254
+00:10:14,000 --> 00:10:17,000
+it's not always for your use.
+
+255
+00:10:17,000 --> 00:10:18,000
+Sometime you create libraries
+
+256
+00:10:18,000 --> 00:10:20,000
+so that others can use your files.
+
+257
+00:10:20,000 --> 00:10:23,000
+Now, in this case as well you will create a package,
+
+258
+00:10:23,000 --> 00:10:26,000
+and then you will give your package to others.
+
+259
+00:10:26,000 --> 00:10:28,000
+The only thing is when you are sharing your package
+
+260
+00:10:28,000 --> 00:10:31,000
+to the entire world it should be unique,
+
+261
+00:10:31,000 --> 00:10:32,000
+it should have a unique name.
+
+262
+00:10:32,000 --> 00:10:33,000
+Let me show you something.
+
+263
+00:10:33,000 --> 00:10:35,000
+I will go to a website.
+
+264
+00:10:35,000 --> 00:10:36,000
+Now, this is one of the website
+
+265
+00:10:36,000 --> 00:10:39,000
+where you can get the libraries.
+
+266
+00:10:39,000 --> 00:10:42,000
+Now, library simply means if you want to do something,
+
+267
+00:10:42,000 --> 00:10:45,000
+and if you don't want to write the code entirely by yourself
+
+268
+00:10:45,000 --> 00:10:47,000
+you can use some libraries.
+
+269
+00:10:47,000 --> 00:10:49,000
+And most of the time we do that.
+
+270
+00:10:49,000 --> 00:10:51,000
+Example, let's say if I want to connect my application
+
+271
+00:10:51,000 --> 00:10:53,000
+with MongoDB, which is a database.
+
+272
+00:10:53,000 --> 00:10:55,000
+So, I can simply search for mongodb-driver-sync.
+
+273
+00:10:55,000 --> 00:10:58,000
+This is a driver which we use to connect Java with MongoDB.
+
+274
+00:10:58,000 --> 00:11:01,000
+So, you can use this package in your project.
+
+275
+00:11:01,000 --> 00:11:03,000
+Okay, let me select a version.
+
+276
+00:11:03,000 --> 00:11:07,000
+So, this is the package, okay?
+
+277
+00:11:07,000 --> 00:11:10,000
+Now, the thing is when we talk about this package
+
+278
+00:11:10,000 --> 00:11:11,000
+what should be name of it?
+
+279
+00:11:11,000 --> 00:11:14,000
+So, this name should be unique on the internet.
+
+280
+00:11:14,000 --> 00:11:16,000
+Now, how will you make something unique?
+
+281
+00:11:16,000 --> 00:11:17,000
+That's the tricky point, right?
+
+282
+00:11:17,000 --> 00:11:20,000
+So, when you are creating a project
+
+283
+00:11:20,000 --> 00:11:21,000
+how will you make it unique?
+
+284
+00:11:21,000 --> 00:11:24,000
+So, one way to do that is by reversing your domain name.
+
+285
+00:11:24,000 --> 00:11:24,000
+That's right.
+
+286
+00:11:24,000 --> 00:11:26,000
+Of course, right, when you're building a library
+
+287
+00:11:26,000 --> 00:11:29,000
+you will also have your website, your company website maybe.
+
+288
+00:11:29,000 --> 00:11:31,000
+So, let's say if we talk about a company like Google.
+
+289
+00:11:31,000 --> 00:11:34,000
+So, if I'm working for Google and if I'm creating a library,
+
+290
+00:11:34,000 --> 00:11:36,000
+so what I will do is I will name,
+
+291
+00:11:36,000 --> 00:11:38,000
+I will say this belongs to a package.
+
+292
+00:11:38,000 --> 00:11:41,000
+So, if I'm making a project for let's say Google
+
+293
+00:11:41,000 --> 00:11:44,000
+and I'm making a calculator or advanced calculator,
+
+294
+00:11:44,000 --> 00:11:49,000
+I will say com.google.calculation.
+
+295
+00:11:49,000 --> 00:11:50,000
+Now, this is my package name, okay?
+
+296
+00:11:50,000 --> 00:11:53,000
+So, by making com.google I'm making sure
+
+297
+00:11:53,000 --> 00:11:54,000
+it is unique, right?
+
+298
+00:11:54,000 --> 00:11:56,000
+Only Google can own this domain, right?
+
+299
+00:11:56,000 --> 00:11:57,000
+It's their domain.
+
+300
+00:11:57,000 --> 00:11:58,000
+So, that's how you do that.
+
+301
+00:11:58,000 --> 00:12:00,000
+So, depending upon your project
+
+302
+00:12:00,000 --> 00:12:01,000
+you will see these type of packages.
+
+303
+00:12:01,000 --> 00:12:04,000
+In fact, in future videos we will be using some packages
+
+304
+00:12:04,000 --> 00:12:06,000
+which have com. something.
+
+305
+00:12:06,000 --> 00:12:08,000
+It means they have just reverse the domain name
+
+306
+00:12:08,000 --> 00:12:09,000
+just to make it unique.
+
+307
+00:12:09,000 --> 00:12:10,000
+But again, for learning purpose
+
+308
+00:12:10,000 --> 00:12:12,000
+you can name your package anything you want.
+
+309
+00:12:12,000 --> 00:12:15,000
+Example, the way we are doing here, package other,
+
+310
+00:12:15,000 --> 00:12:17,000
+but it should have a meaning that's important.
+
+311
+00:12:17,000 --> 00:12:18,000
+So, yeah, that's about packages.
+
+312
+00:12:18,000 --> 00:12:20,000
+Don't worry, we'll use packages more.
+
+313
+00:12:20,000 --> 00:12:23,000
+In the upcoming videos it will make much more sense.
+