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Hello, Jim.

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So they were going to run with you with the glasses.

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We'll talk about what glass can contain on good examples.

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We learn what our fields and utilization logs, constructors methods and nested classes.

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I'm going to explain to you what getters and setters are and how we can use them.

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We are going to create our own class and we'll create object of our custom class together.

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Let's start from the previous lesson.

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You already know that class is our template for objects, but what does it consist of?

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Glass can contain constructors, fields, methods and utilization blocks and nested classes to understand

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and better.

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Let's jump to example.

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Let's imagine we are implementing online store and we need to implement our virtual card for shopping.

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You already know OPIS and you know that everything is an object.

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Take into account we expect multiple users on our website.

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We are going to have a lot of cards.

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We need to have a template for card object.

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That's why we need to create card class.

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Here's card class.

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I created it beforehand to save time during this video lesson.

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I will walk you through it line by line.

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Our goal now to understand what class can contain.

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First of all, class can contain fields.

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Often fields are called properties.

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With the help of the fields we can express state of specific object fields can have different modifiers.

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For example, fields can be static and non static, final and non final.

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We are going to have separate lesson about static keyword and static elements in Java and we'll discuss

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final keywords.

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Also in separate lesson, this lesson only about classes.

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So this is all fields which we have in our class.

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Class also can contain initialization blocks.

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We may have static and on static initialization blocks.

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Why do we need them?

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For example, I have some fields which I want to be initialized with values by default.

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In this case, every timecards object will be created.

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Card counter will be incremented in case cards will be created without user i.e. I know that I need

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to sign this card to some user.

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Let it be special user with ID one and one of the properties has tax time.

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This is also custom type described by us.

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I will show it to you later in this lesson.

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But now imagine that you have this field and you don't want to leave it, not initialized.

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What default value has all reference types of data?

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No.

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And according to logic that I implemented, I know that tax should not be known to avoid no pointer

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exception because I use this variable in court below and b what stands for null pointer exception,

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one of the most widespread exception which happens when you call method or new value.

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That's why it's called no pointer exception.

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We'll learn more about exceptions in separate section.

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For now, I want at least some default value should be assigned to this variable.

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That is exactly what I'm doing here.

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I using this civilization look to initialize this field, the similar situation with our discount object.

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I initialize this field to make sure it won't be no talking about starting blocks, it is worth to mention

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that they are very narrow application domain Whiskas class example.

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It was hard for me to come up with the example of static initialization block.

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This block will be executed only once one class will be uploaded into GBM.

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In this case we just write text to console.

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Good example of static Blokland civilization usage is driver classis.

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You always need to register driver in the system so it would be comfortable to use static initialization

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work for this.

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For example, once driver class is uploaded into GBM, we can register it in some services.

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This is a real life example which we will see later in this course.

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But now you at least understand how potentially we can use static in civilization.

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Bloks problems it again.

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Universalization looks let's move on may contain constructor's constructor is a special method which

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should be called to instantiate object.

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Important things to mention about the constructor constructor name should always be the same as class

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name.

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If your class name is called, then constructor is also called rule about writing.

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Method starting from lowercase is not applied to constructors.

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It doesn't have return type.

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You remember that all method should have return type in constructor.

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You should not specify return time because constructors always by default return reference to the object

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and keep memory.

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You always have constructor by default.

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Let me show you this.

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Even if I wouldn't have this constructors, I would still have default one.

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Let me comment on this court and now let's jump to the demo file and create card object.

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Let me declare a variable of type card and assign cards.

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Object to it.

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The great object I write new keyword.

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This is a common to Java to allocate memory for object in here and after that I call constructor and

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print cards object to cancel.

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Let's run this program.

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And here we are, you see that quote from Start, a conservation blog executed first, and here's our

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character object printed to console.

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Now let me create custom constructor.

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Let's pretend I want to create card with specified cartridges and user aguy.

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And when I created custom constructor, there is no default constructor anymore.

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And here is see compilation error.

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The constructor card is undefined.

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That's why if you want to declare a custom constructor and keep constructor by default, you should

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specified explicitly when I am Corman's, this constructor compilation error is gone.

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Let's take a look how we can use custom constructor.

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We know that our constructor can take two integers as arguments and you see that the first parameter

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will be assigned to a property of this object in the second parameter will be assigned to user the property

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of the current object.

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You can see that I use this keyword to reference current object because this idea, if this property

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in card object and ID is just a local variable of the constructor, that that makes sense.

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So inside the class you have keywords which always reference to the specific object.

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Now you can call your custom constructor like this new card and parse constructor arguments when we

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bring second car token.

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So you can see that IJI and user idea of this class is different from the first class object.

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Now, when you know what the constructor's, you might be wondering why do we need initialization blocks

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if they have constructor's on this example, you can see that no matter which constructor will be called

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utilisation, LOC will be executed.

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In both cases.

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Knowing this, you can use initialization blocks to put their code, which you want to execute no matter

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what constructor will be called.

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Is it clear now what else our class can have?

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Our class can have methods.

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That is behavior of our object.

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For example, our cars can add new product to the cart.

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Let's not get deep dive into the logic here.

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I will share with you source code of this lesson and you will be able to take a look miserably at implementation.

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But now let's understand that methods are behavior of our object and can change state of our object.

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And now you can understand the difference between method and function.

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Function can exist without object independently.

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Method is the behavior of the object.

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That's why in Olby we call specific box of code, which can be invoked by their names methods but not

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functions methods.

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This is something that is always associated with an object.

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In this particular example, our card contains an array of products and we can add product to this card,

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namely to this array of products.

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That is exactly what this method does.

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It adds new product and change the state of our cart.

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Notice that each time new product is added to the cart, other methods are called to calculate total

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net price and total gross price.

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These are two private methods.

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That means nobody outside this class can call these methods.

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I can call these methods from this class.

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Only X modifiers will be covered in detail in encapsulation.

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Lesson in your code method and location might look like this.

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You created car to object and after that use its behavior to add product to the cart products is also

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our custom class.

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By the way, here it is, just two properties for the sake of our example.

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And he seemed concerned that after we added two products, total net price, total gross price and total

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tax have been changed.

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After these methods, I have other methods that are called getters and setters, why do we need them?

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You see that all properties of cart objects are private.

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That is because I want to have full control over how people can interact with my object and how they

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can change.

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State of object was usually used to rid properties of objects.

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You can be 100 if we are making our properties private so nobody could access them and change them,

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then why do we need to create better sensors?

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Let me explain you on this example.

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You can create together and return your products array, but this means that everybody who has links

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to your products array can change state of disarray.

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Just using this reference, for example, having reference to products, every object I can add to more

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products in it and state of the card will be different.

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In this case, there would be two more products in CART, but now when you can write code of your car,

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you can say that you want to give reference to this array.

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Everyone who wants to investigate state of products are we can do this and you can return a copy of

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the script by doing this.

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You can be sure that even if in some other places reference to products that will be obtained, they

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will get reference to the copy of your and won't be able to change state of our regional products away

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from your car.

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This is critical for us because based on the products from this array, we calculate total net and total

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gross price.

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Imagine that somebody would take the reference to products are a few more products to it without recalculate

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total net and gross price and would just proceed to checkout with this car.

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Customers would be happy that they got more items for free, but our management definitely won't be

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happy.

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And if I don't want that somebody said a completely new array of products in my car, I just don't create

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Setar.

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That's it.

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But if you have Setar, you can verify arguments to make sure that they are valid.

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According to our business logic, for example, everyone can, said Cartledge here, but nobody can

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set a value less than zero because I wrote the code to verify this in case I'd is less than zero.

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Just exit from this method and you can see that Rejon keyword is also used to exit method in both methods.

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Even when you don't have intention to return some value from method or like here, for example, anybody

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can add product to the cart.

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But in case somebody is trying to add no into my array, I don't allow to do this and exit from method.

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Remember that validation of all arguments which were passed to the method if the rule which you always

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must follow.

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By the way, if you want easily generated getters and setters, use next hotkey old shift s and select

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generate getters and setters.

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You can select fields for which you need getters and setters or only getters.

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For example, if you don't want the grade setters and vice versa, press generate to generate code.

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I already have all necessary getters and setters.

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That is why I wouldn't press this button.

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Now, in case you forgot hotkeys press mouse right.

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Click select source and then generate getters and setters.

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We have to string method here, we are going to talk about this method in details in the lesson about

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object class.

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But in the meantime, let me explain you what this method is about in a few words in Arkansas here we

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see text representation of our the object.

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That is because to string method is overridden here.

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And you can see how the string is created from combination of fields from our car object when we pass

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reference type to Winterland, method to string method call is invisible for us and when to string method

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is called this code is executed and this string is returned.

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That's why we see rideable representation of our card object to generate to string method use the same

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hotkey as we discussed earlier, all shifts and select generate to string.

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It says that I already have two string but still I want to show you details you can select which fields

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methods you would like to use to create string which will be returned after the string method call.

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Besides what we have already discussed, glasses can also contain nested glasses, nested glasses can

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be static and non static, static nested glasses, usually called just nested static glasses and nested,

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not static glasses, usually called inner glasses.

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And here you see discount untax glasses we use for both of these types in our cars glass.

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And I believe you remember the beginning reinitialize variables of these types with default values in

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our initialization lock to not overwhelm you with information.

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In this lesson, let's agree to learn types of classes in the separate lesson.

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For now, let's repeat one more time.

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One glass can contain glass, can contain fildes, initialization blocks, constructors methods, nested

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classes.

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And we know that nested classes could be nested static classes and in their classes.

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I will share with you links to the source code in attachments to this lesson so you can review it one

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more time.

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Method classes will be discussed in the separate lesson.

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And now let's review what we have learned today.

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Today we learned what class can contain and how to create our custom objects.

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Now you know the difference between a method and a function, really, of the concept of getters and

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setters and how to generate them easily in eclipse.

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Take a look one more time in the source code of examples which we reviewed during the lesson and be

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prepared for the next lesson.

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Thank you for your attention and see you in the next lesson.