19 - Java Collections Framework/012 Queue and Deque_en.srt

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Hello, Jim.

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Today, we are going to lunch with you and other collections of Iraq.

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Today we'll talk about you interface and one more important interface that extends you, that is that

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interface with the masses in interface.

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And I hope you didn't skip lessons because in previous lessons during the General Overy, we already

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talked about you and discussed Masset that this interface has.

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But today we'll dive into the details.

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After that, we'll learn methods in that interface.

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Today, we're going to learn what is the difference between these two interfaces.

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Also, we'll learn what FTF old principle is and what LIFO principle is.

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After we learn interfaces, we'll take a look at the most popular Q and deck implementations.

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And I will share with you practical tips and practical cases.

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And at the end of the lesson, we are going to review your home task and I will explain how you can

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practice your skills.

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Let's start and to understand what CU is, we have to understand what FTF old principle is.

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If you don't skip lessons, then you remember that FCF also is a method of organizing of a data structure

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where the first elements that enter the queue, the first leifs is a Q, in other words, the head of

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the queue always processed first f i f o stands for first in first out here on the slide you may see

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brutalisation of the Q the Q has the head and the tail.

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Students usually wondered where the heart of the Q is and where style of the Q by convention.

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The end of the queue at which elements are added is called the tail back Oriya of the Q The end at which

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elements are removed is called the hat or front of the Q.

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Analogously two words used when people line up to wait for goods or services.

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Does it make sense now?

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If yes, then let's answer our next question.

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Where Q is used.

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Imagine that you have two services.

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The first service is in charge of onboarding of new customer.

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This service process information about the user verifies his payment method at him to the theorem,

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checks whether this user already registered, etc. Let's call it onboarding service.

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And another service is in charge of handling all payments from the user for his subscription on a monthly

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basis.

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Let's call this payment service.

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Those are two independent services because the first one is in charge of selling subscriptions to customer

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only on one side.

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But they are different of the similar marketing sites that promotes different products and services

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of the company.

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Our onboarding service is one out of many services, but the service that is responsible for charging

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clients on a monthly basis is used by all websites and systems within the same company.

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This is real life scenarios that my team implemented in simplified form also.

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But still, I believe you got my point.

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And before process payment information from any of the website, the queue exists.

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It exists right in the middle between all services and charge and service and all services, including

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our onboarding service submits the message in the queue.

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The message contains payment profile of our customer and product details and our payment service process.

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All these messages one by one and implements all necessary logic related for recurring payments.

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Does it make more sense now?

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Can you understand now?

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Why do we need Kyuss hope?

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This brings more clarity and you understand why we need to use Qs.

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OK, if you understood cuz let's understand what a deck is and to understand that we have to understand

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what LIFO principle is.

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LIFO is a method of organizing the manipulation of a data, whereas the last element that entered the

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container should be processed first.

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LIFO stands for Last In, First Out.

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If you remember stack class that extends vector, that is also implementation of LIFO principle.

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And on the screen you can see visualisation of stack.

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But where we might want to apply LIFO principle, the easiest example of that usage, which you are

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faced with on a daily basis, is in the clips.

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Have you ever used and do operations in Eclipse?

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How do you think the operation works?

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Each batch of changes is put in the stack and then the case and those short cards is correct.

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The latest separation is removed from the stack.

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For example, you wrote Hello World.

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The World World is on top of your stack.

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When you want to run the operation, it leaves the stack first.

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Or imagine your browser history.

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You open new pages and then you need.

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The return on the previous page or asset allocation in your Java program, we can call one message from

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another one and after that call one more method how to track the flow of program execution only with

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the help of the stack data structure that stores elements according to LIFO method that it makes more

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sense.

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Now, can you understand now when do we need stack?

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Awesome.

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And now when you understood what CU and DEC is and why we need them, I suggest dive deeper into the

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details and learn interfaces.

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Here is a new interface we have at and of a message here.

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Both exist to add elements to the queue.

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Both returns through in case element was added to the queue.

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Then why do we need two similar methods and why do we need add method here?

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If it is present in collection interface?

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Let's understand the difference at that is present in queue interface to highlight the specific behavior

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of that method in queue type add method adds elements to the queue.

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But as you can see from the documentation here in legal state, exceptions will be thrown in case element

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couldn't be added because of the capacity restrictions.

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To be honest, in most of the cases you wouldn't see this error while working with the implementation

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of the queue interface.

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Why?

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Because most of the implementations have no restrictions on capacity and their unbounded.

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And in this case there is no difference between at and of.

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A method of a method doesn't throw exception in case element is not added because of the capacity restrictions.

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It also can return false hope.

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This knowledge will help you during the interview, in case you will be asked what the difference is

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between add and offer method in queue interface.

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Let's move on.

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We have two methods to retrieve elements from the heart of the queue and remove it from the queue.

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Zaya, remove and pull.

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The only difference between them is the way how they behave in case there are no more elements in the

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queue.

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Remove Masset in this case will throw no such element exception and Paul MassArt will just returns.

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And now what do you see in real life?

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I would say evaluate the logic of execution of your program.

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First, in case you would ask me what method I would use, I would use full method and would just perform

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null check.

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I just afraid of all exceptions and I would rather opt for options.

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That doesn't throw an exception, but all cases and programming styles are different and I can accept

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that.

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And that's why it's up to you.

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Which method to choose is a similar situation with the next two methods.

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We have two methods that allows us to get the elements from the head of the queue, but that don't remove

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element from the queue zaya element and pick.

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The only difference is that element Masad Maestro.

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No such element exception in case there is no more aliments and big method would just return.

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Now you already know what I would choose.

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That's all methods that are declared in queue interface.

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Let's move further and let's investigate what message do we have in that interface.

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So as we already discussed, that extends queue interface and organizes data according to LIFG principle.

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Let's review methods now that are present here in the top of our list.

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We can find a lot of similar methods that can work with the head and with the tail of the queue at first

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and at last of a first and of last.

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Remove first and remove last, both first and last week first and pick last.

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I believe it is clear how they work.

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Since we discussed similar methods in queue interface, I noticed that there is no element first and

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element last method if to follow the analogy in is naming.

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But do we have methods that doesn't remove element from the queue and throws an exception in case there

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is no element?

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Yes, we have aget first and last method here.

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They here also to interest in masses, remove first Securus and remove last appearance.

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When we are referring to the first occurrence, we mean first in case we would reverse elements from

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the had the tail.

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So the first Securus will be closer to the heart of the queue and the last appearance is closer to the

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tail of the queue.

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After that abasic message from the queue go here and en masse, it adds all elements to the container,

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the same as it is declared in connection interface.

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There is only one clarification that all elements will be inserted into the end of the queue.

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And here are static methods.

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We already discussed what the stack is and here's a mass to manage stack push.

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It adds element in the heart of the queue.

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This method will throw illegal state exception in the case.

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Element can't be added due to capacity restrictions.

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This method is similar to at first method.

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This is even specified in general documentation.

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Then why do we need it at all?

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For compatibility reasons with legacy class stack, the push and pop methods exist.

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This means that they're only to make a transition of all code easier for programa.

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The pop method is here and it is equivalent of remove first MassArt.

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And I believe you already understood why Oracle left this method in this interface.

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The last message that we didn't talk about is the sending iterator.

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This message, according to the interface, should return iterator objects that can iterate over the

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elements in reverse sequential order.

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That is from the last element from our tail to the first element to our hat.

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That's all matters that we have in our back interface.

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Now let's investigate the most popular Q and deck implementations.

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On this slide, you can see the most popular implementations of Q and back interfaces, I recommend

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you post the video and read the slide attentively.

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I believe there is no need to investigate each of these class in details.

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It is better to put our focus on the most popular implementations, the most popular implementation,

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in my opinion, and based on the official Oracle tutorials can be split in two major categories implementations

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of the interface and implementations of just rescue interface.

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In case you need the implementations, then most likely you will be happy with slinked list or array

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that class.

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If you need Q implementations, most likely you will opt for lenth list of priority queue if you need

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thread safe implementations of the queue.

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I would like to draw attention to avoid blocking Q and priority blocking queue.

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If you need thread safe implementations of DEC, then your choice is linked lock and DEC.

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As you can see there is really a lot of options.

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But in my opinion and based on my experience in 95 percent of cases when you would need to use DEC implementation

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to implement some stack or in case you would need Q you would use in case class the rest five percent

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of cases is for thread safe implementation of the Q and DEC and also priority.

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Q taking into account we already had lesson about Lindley's and we already learned the Q and DEC interfaces.

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There will be nothing hard for you just to call these methods on linked list.

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And that is why, for the sake of the demo, I would like to show you how AQ works on the example of

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priority.

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Q So here I prepared them file.

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I will leave link to this file in attachments to the lesson so that you could copy and run this file

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on your local computer.

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Here I declare it variable of type.

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Q Parametrized with the integer type here I created object of.

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Q And in these lines you can see that I added to the Q five elements.

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They are two eight three one then.

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So in the case I'd like to take the first element in the Q what it would be.

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Take your time to think about this question because this is a trick question.

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We all know how Q works and what is a five for principle, but priority Q has interesting feature.

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It automatically source elements according to the natural order.

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I hope you didn't skip the lesson about comparator uncomparable.

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And you know that natural order is an order that is described in the compared to method because of implementation

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of comparable interface.

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And that's where a provocative word comes from in the name of the Q it prioritize elements.

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So in case I would prefer to control the elements from the head of the Q this would be one even despite

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integer object was well your one wasn't inserted the first.

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Let me run the program to show you this.

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I used polymathic to get elements from the Q and remove it.

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So the size of the Q right now is four now in case I call Big Masset and get the hell out of the Q,

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but don't remove element here.

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You can see in console output that our next object and our priority.

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Q is to and the size of the peak.

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It is still four because I didn't remove elements from the Q Pay attention to the fact that all elements

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that you put into the priority.

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Q should implement comparable interface because in case type doesn't implement comparable interface,

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Breuer's UCU object would throw exception, glossiest exception that would say that your type cannot

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be cast to comparable type.

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Let me show you an example.

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Let me comment these lines of code here, you can see that I create Q Parametrized by product type.

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Just to remind you, product is our custom type that we created during our work on online store implementation.

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After that, I want to place my product into this.

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Q Let me run the program to show you what would happen and here you can see glass cast exception.

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What to do now?

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We have two options here.

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The first one is to use only types that implement comparable interface.

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The second option is to set our priority.

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Q How to compare elements.

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Let me comment these lines of code to show you the next example here.

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You can see that I created the same Q Parametrized by product type, but I pass the product comparison

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to the constructor of prosecute.

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Now my project knows how to compare products and saw them let me run the program and we can't see error

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anymore.

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That is because our Q knows how to prioritize products, where to use priority.

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Q Imagine that you want to implement helpdesk during the day.

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You receive tons of requests and complaints, but you have limited number of operators in your company

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that can.

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These requests and you have special app for your operators where each operator can click a button,

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they can request and move it in progress, and it is obvious that most critical requests should be processed

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first in case a customer can't make a payment in the online store or customer already paid.

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But some error happened and he or she can't get details of his order.

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That is more critical than some random question, like one sorting by manufacturer will be implemented

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on your site.

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They agree with me and what you have to do probably on the front end, you would implement some dropdown

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where you would ask your customer to categorize request.

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For example, here on the slide you can see example of support of Panya in your system.

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You have some object, something like support ticket type.

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You also have to implement logic that would assign support ticket type.

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And based on the type of the request, you would assign priority, high, medium or low.

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And after that you would pull your support ticket object into the queue.

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And you already know that we have to either implement compatible interface in our support ticket or

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we have to create a competitor and pass it to priority queue.

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Interesting.

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I hope it is.

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And moreover, implementing something like this already a real life task for our software engineer.

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This will be your homework.

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But before I would share with you the details of your homework, let's recap what we have learned today.

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Today we learned Q and DEC interfaces.

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We learned in detail how matters that are described in these interfaces work.

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We learned what a FFO and LIFO data store methods are.

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We used you and DEC implementations and learned the most popular ones after that.

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On the real example, we learned how particular works and now I suggest reviewing your homework.

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You have to implement helpdesk facades that would serve as a main interface for a support engineer to

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interact with the system, helpdesk facade interface has only three masses that you support.

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You could get next support ticket and get a number of tickets according to our requirements, get next

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support ticket.

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Masset will be called when your support engineer would click on the button.

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This message should return top priority item.

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I almost explained to you how to implement Help Desk in the online store.

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Here you can find the details about what request type might be and priority for specific request type

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during the creation of the support ticket will specify only typos request and its priority is defined

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automatically based on the Moppin that are written down in the table.

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And there is one more requirement in the case.

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Support tickets have the same priority.

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The one that was created earlier should be processed first.

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I can give you a small hint here.

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You can implement counter.

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This even might be static field and you may consider the value of this field when you would compare

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to support tickets, for example.

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Does it make sense home?

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The task is clear for you.

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This is a really interesting task that will help you a lot in understanding of the cues and will give

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you some clues to real life experience.

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Thank you all for your attention.

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Have a great day and see you in the next lesson.