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Hello, Jim.

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In this lesson, I'll go to understand the main descendants of collection interface before going deep,

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I believe it is very important to understand the big picture and learn three main interfaces in collections.

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Iraqi today will hold a high level overview of such interfaces likely set.

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And Q According to our agenda, we are going to start from the overview of the class diagram of collection

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interface with its main descendants.

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After that, I'm going to explain in simple words what a key difference is between three interfaces

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and why we need them.

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I will explain you what list is said and Q You use the explanation of the cube.

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We are going to learn what f i f o principle is.

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This lesson will help you to understand the first structure of our lessons and understand the core hierarchy

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of collections.

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Let's start here is our class diagram.

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This one is the extended version of the one you saw in the previous lesson.

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I believe you are already familiar with the collection interface.

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Now let's look at the most popular child interfaces of collection interface that we are going to learn.

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There are three interfaces that extends collection interface and that implemented by all the collection

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implementations in GDP, Zaya least set and Q They're all collections.

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But each interface is introduced in behavior on the quality of implementation of collection interface

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by extending it.

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Why do we need this interfaces?

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Let me briefly go over each one.

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Let's start from the least interface.

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You already know that collection is just a back where you can put all your elements.

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The list interface.

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Introduce an ordered collection with the possibility to manage your elements by the index.

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In the more simple words list is an order.

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A collection of elements was all benefit.

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That follows from that statement.

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We can add element to the specific index and the collection.

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We can get element by its index and we can replace existing element as a specific position to set the

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new element in the specific position we have to use, said Mass.

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With a specific index and element.

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If we want, we can remove the element from the specific position in our list.

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We can get the index of the first occurrence of the element in the specific collection and index of

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the last occurrence of the specific element to perform these tasks.

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Mass index of and last index should help us at least also allows us to get list iterator list iterator

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that this extended version of the regular iterator in the separate class in about iterators.

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And we'll explain the difference.

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Sometimes we may want to create some lists, for example, to process back amount of data.

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We may split our list into four equal chunks and perform any operations we need in four separate sets

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of execution.

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I believe you are aware that Java supports MultiThreaded and a bit later in the course, I'm also going

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to teach you that.

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Besides new absurd methods that were introduced, there are also to default matters that are absent

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in connection interface and that are present in the list interface.

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Zaya, replace all MassArt.

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This method will take a function that can transform an element of one type to the element of the same

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type.

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We may want to use this method when we want, for example, transform all string objects in the list

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to the string objects in the lowercase.

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Sort method allows us to set the algorithm and to tell exactly how we want to certain elements in the

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list, a bit later we're going to run such a functional interface as comparator.

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Now, let's proceed with the collections Iraqi.

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Let's talk about set interface.

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What do you think?

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What new methods are introduced in the set interface in comparison with collection interface?

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No one is a set interface, doesn't introduce new methods.

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Then why do we need it at all?

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Let's recall what a set is from the mathematics.

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The set is a well defined collection of discrete.

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The set is a well defined collection of distinct objects.

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The set interface is a main interface for the Iraqi of containers.

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By the way, collections are often called containers.

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So set is the main interface for the hierarchy of containers that contains only unique elements that

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different implementations of the set interface during the development of JDK engineers come up with

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the decisions that they need to distinguish a collection of elements and the set of elements.

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Somehow the best decision was to introduce new interface.

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So you're of development.

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Engineers may declare variable of type set that would give us new methods to manipulate with elements

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in the container.

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But this instantly will give us the vision that this container contains only unique elements.

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To understand how implementations of the set interface work, we need to learn map interfaces first.

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We are going to understand later why.

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And now let's review one more interface Hirschi interface.

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There are a few new abstract methods were introduced here to manage the queue.

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They are offer to insert an element into the queue, remove this method to retrieve and remove the head

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of the queue.

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But in case there is an empty queue, the method throws exception.

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What is an exception?

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And a bit later we are going to learn how Java programs may handle exceptional situations of program

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execution.

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Right now you can understand exception like something what is not an expected way of program execution

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and what may potentially interrupt the program in case there is no code written that handles the exception

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for this method also retrieves and removes the head of the queue the same as remove method, but with

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only one difference in case queue is empty, there is no exception, no value is returned instead.

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Element this MassArt retrieves but doesn't remove elements from the Q the same as remove method, it

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throws exception in the case.

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Q is empty.

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Take Macit also retrieved but doesn't remove elements from the cube, with only one exception, that

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in case there is an empty cube, no value is returned.

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That's all new methods that were introduced in Q interface, no other default methods were introduced,

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cues needed when you need to implement first in, first out principle, so-called f i f o principle,

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imagine that you process support requests and you need to process them in the specific priority.

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And according to the date, when you receive them the support you get that you received the earliest.

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Exactly.

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These tickets should be processed first.

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And here you can understand what the queue is.

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The first support that was received by Q The first left in the queue.

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I feel really prepared.

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Super interesting home task for you to improve our online store and to practice your skills in writing

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use, but that will be later.

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So right now I believe you understood the three main sub Iraqis that goes right after collection interface.

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And also the structure of the next lesson should be clearer for you now during the next lesson.

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So we are going to learn each interface in detail with all methods and to learn the most popular implementation

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of each interface.

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I want you to understand, Siiri, first before we start calling.

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Believe me, this is very important.

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But very soon you would beg me to stop quoting examples, I promise you.

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Now, let's review what we have learned today.

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Today we have learned what has remained descendants of collection interface.

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Now you know why we need at least set new interfaces.

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Moreover, after this lesson, you may understand the difference between them while explaining what

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A is.

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We learned f o principle.

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Now you are ready for the next lesson.

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Thanks a lot for your attention.

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See you in the next lesson.