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Hello.

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Students, in this lesson, we are going to learn what connections are.

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This is very important topic because connection interface is implemented by all connections implementations

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in Java.

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That's why understanding of collection interface is a key for understanding of all other collections

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in Java.

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So today our primary focus is learning of collection interface.

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I'm going to show you your middle class diagram, will understand what it is and how we can use it in

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the future.

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To understand a type structure during the lesson will understand what methods collection interface has

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and why do we need them.

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We will review abstract and default methods of collection interface and at the end of the lesson, we'll

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look at the collection source code.

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Let's start.

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I suggest that our lesson from this slide on this slide, you may see visualization of what the collection

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is to understand collection.

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Imagine the back, the big back where you may put all your stuff.

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You might put your product, user card and all other objects, and you can retrieve exactly user or

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product or cards by its index like you did in array.

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What you can do is to put all things from your back on the floor and go over them one by one.

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We're also going to learn in the separate lessons, the specific type that is developed to go over each

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element.

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What else we can do with these?

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Back to answer this question, let's take a look at collection interface and we'll learn what else we

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can do with our bag of elements.

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Here is a class diagram we are going to learn with your UML language that is unified model and language

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in detail a bit later.

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But this is what is used to call class diagram.

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And while being a software engineer, you are going to see such diagrams very often.

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What do we have here?

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We can see that collection interface extends a terrible interface, a terrible interface.

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We are going to learn in a separate lesson, the same as Iterator.

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But in short, this is an interface that stands on top of all collections interfaces to make sure that

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it will be possible to iterate over each element in each implementation of collection interface.

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Today we are going to focus on collection interface and we will start learning it from this class diagram.

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Let me give you a quick introduction regarding symbols here.

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You can find indication whether this type interface or no, that is our interface text right above the

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interface name.

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We can see that it's Arabel and collections, both interfaces here.

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We can see list of methods that each specific type has, plus some means that this method is public.

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After that goes method signature.

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That is method, name and method parameters followed by colon.

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And we can find return type right after the column.

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For example, the first method in the list in collection interface is this method without parameters

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that returns in value.

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Does it make sense now?

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This knowledge will help you to understand class diagrams written down on human language.

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And let's answer our original question.

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What else we can do with this back?

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We can check a number of elements in it.

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That is what size method does.

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We can check if this bag is empty or no.

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We can check if this bag is empty or no.

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That's why when it is empty, we can ask our back elements, does it contain some specific element or

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no contains measures that will help us with this task.

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We have also matters that control collection of elements, interior objects and methods that can turn

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collection of elements into the array of specific types.

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For example, if your collection contains only elements of product type, we can convert our collection

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into of product elements, but not in the array of objects.

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If you don't want, can you feel the difference?

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After that?

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We can see methods that we already kind of discuss.

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Let us add methods.

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I can add elements to the collection.

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I can also remove elements from the collection and to remove elements from the collection, I have to

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pass this exact element.

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Another important behavior, we can check whether this collection contains all elements that other collection

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has.

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That is our contains all method.

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We can add all elements from one collection to another.

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To do this, we have to use at all method and we can remove all elements from the current collections

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and other collection has that is our remove all method and believe you can see on the slide that message

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that we have just discussed.

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Take out the collection as my argument.

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If you want, you can keep only elements that are present in both collections.

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To do this, we have to invoke retain all methods and positive reference to another collection into

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it.

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In other words, this message removes from the current collection all elements that are not present

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in the collection that we passed as a method augment the methods that are left here are also describing

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claims method will remove all elements from the collection and as you already know, equals and harsh

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methods that are the methods that each object should have.

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But the idea of specifying equals and Haskett methods in the collection interface is to put stress on

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the fact that these methods should be implemented in an implementation of collection interface and that

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these methods should override default behavior from object class.

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And the last but not the least, massive collection interface is an iterator.

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Pay attention to the iterable interface description now.

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It is also the collection interface because it implements a terrible interface.

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As you can see, Iterator method returns object of iterator type insert.

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This object will help you to iterate over each element in your collection.

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We are going to learn what Iterator is in the separate class and that is how our collection interface

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that is something.

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What do you have to remember?

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We just have such interface and what we can do is just to remember it just as an alphabet.

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We don't ask why a letter is written exactly in this way.

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We just learned that this is a letter and how it sounds.

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And when we know that we start building words with this letter, the same as here, we just have to

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learn collection, interface and learn how to use it.

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So here on the screen, you may see only abstract methods that should be implemented in each collection,

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but there are a few more other default methods in the collection interface.

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What are they to answer this question and to give you otherwise how constantly learn new things and

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check information that you get not only on this lesson but in any tutorial?

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Always investigate the source code of your conversion.

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I believe you remember how to add source code, your code editor and where you might find it.

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Let's open collection type to investigate the source code and find methods that we didn't learn yet.

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I press control shift and simultaneously I have to type collection.

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I need collection from Java with your package and here this and here on the right, we might see a list

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of all methods that are present in this interface.

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It looks like we went over all abstract methods.

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How I learned which method is abstract and it's is a small a letter that stands for abstract.

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But we didn't cover in our presentation methods that have Glitnir.

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What are they?

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Here's the overloaded method to array it.

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Just take specific functions that will describe how to convert collection to a right to be able to apply

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this method.

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We have to know how to write in the functional style in Java and understand what functional interface

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is.

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Don't worry.

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This topic also will be discussed in the separate lesson.

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I just want you to understand, at least on the high level, what these default methods are about.

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Remove method, this method takes predicate, predicate is a specific type that can return true or false

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based on the specific function that you will pass as a method argument to this method.

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It will identify which element should be removed.

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For example, you may describe functions that will return.

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True in a case product price is more than one hundred dollars, and in case this function will be applied

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to this specific product and collection, it will be removed and this function will be applied to each

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element in the collection you might find while loop here and see that Iterator is used to go over the

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collection as a condition for each element in the collection and remove it in case it satisfies the

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condition.

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Also, there is a default method that creates iterator.

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Split Iterator is a specific type that can traverse and make parts of elements of the source collection.

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And here is a method that exists in all implementations of collection.

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Interface Stream Method joins the collection into stream of elements or in other words, sequential

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stream of elements.

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String Mapei was introduced in Java version eight and it was a breakthrough in this course in separate

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lesson will be on stream API and we'll learn how to use it as a practical exercise.

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Will even rewrite our home tasks with the help of the Stream API.

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And here is a massive, transparent stream.

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According to documentation, it returns possible parallel stream with the current collection at its

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source.

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Now, let's recap what we have learned today, so they've learned what the connection is, we try to

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imagine collection is a back for our understanding.

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The day you saw your first UML diagram, class diagram.

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Now you know how to read class diagrams to understand the type of description we reviewed all abstract

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methods in collection interface.

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And after that, we reviewed the collection before methods.

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Also during the lesson we investigated source code of collection interface.

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That's all what I have for you for today.

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Thanks a lot for your attention.

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See you in the next lesson.