WEBVTT

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Hi everyone.

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Welcome back to this tutorial.

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In this tutorial we will code and learn about the map method which is part of the Streams API.

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Before we get to the coding part of it, let's talk about it a bit and then get into the coding part.

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Basically the map method in streams API is used to change the type of the stream from one type to another.

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We have seen some of the examples of the map method before.

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Now we are going to dig in further and then explore the map method.

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Don't get confused.

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This with the map collection that we have as part of the Java APIs.

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Let's go ahead and code this one.

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Let's go to IntelliJ.

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There you go.

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What I'm going to do in the streams package, I'm going to create a class called streams Map, Example

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Streams map Example.

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And then I'm going to make this class executable by adding public static void main.

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There you go.

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Okay.

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The use case that we are going to code here is that we have the student database class, which has all

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the students.

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The use case is to just.

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Elect all these names of the student in a list and then print that list in the console.

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That's a use case that we are going to code.

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So for this purpose, what I'm going to do, I'm going to create a method called.

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Names.

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And then I'm going to make this class, make this method static.

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What is that?

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It is going to return.

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It is going to return a list of string.

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Basically, it is going to just return the current names.

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Right.

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Let me put this in presentation mode.

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So this is going to return this names list.

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The first step is we are going to get the list of students.

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You can get that by calling student database dot get all students.

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So this is going to give you the list of all the students.

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The next step is we are going to create the string.

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That's right.

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What is the next step?

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The next step is we are going to explore the map method.

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So we have lot of methods which are part of the stream, but the method that we are going to be using

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here is the map method.

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The map method.

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If you take a look at it, it accepts a function.

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So function we are going to implement it by using the method reference.

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What is the function in general?

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It is going to take in a type and then it is going to return a type, right?

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So here the input is going to be the student, but the output that we need is just the names, right?

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So how we can implement that.

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A student.

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Colon.

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Colon.

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And then.

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Let's import the student.

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As soon as you.

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Press control space here.

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You're going to get all these recommendations.

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What is that we are going to be focusing on?

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We are going to be focusing on the name.

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So here what is happening is just going to comment it here.

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So you're getting the student as an input.

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And then the output is going to be the student name, not the whole student object.

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The student object is coming as an input to this map method, we are mapping that student.

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We are transforming that student object to a name which is of type string.

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So if we go and take a look at the name, the name is of type string.

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So.

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The output of this one is.

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Stream of.

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Shouldn't.

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The output of this one is.

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Stream of string.

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So this map method is converting the student object to a string object.

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And what we are going to do, we are going to collect this whole stream of string.

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Your list.

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That's what we are going to do list.

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And then if you take a look at it, there is a static import java.util stream dot collectors to list.

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So we are going to use the collectors to list method in order to collect all the names as a list.

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There you go.

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Now, what I'm going to do, I can either add a written statement here is going to work, or what we

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can do is we can add a list of string in here.

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What we are going to do, we are going to add the.

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Name a student list equal to.

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And then we will return this.

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Either way is fine.

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You can either add the return statement directly here or you can assign the result to a list and then

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return it.

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Now what I'm going to do, I'm going to print this.

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I'm going to.

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Print the names list.

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Good, Right.

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Let's run this one.

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So what is the result of this one?

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It is going to give you the list of string.

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Right.

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Let's run this one.

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We run this.

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It is going to just give you the names of the student as a list.

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So the map method is basically used to convert from one type to another type.

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It is not just that.

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I'm going to add some enhancements to this use case, which we just coded.

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What I'm going to do is.

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I'm going to perform some operation on this one.

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So here we are getting this name right, which is of type string.

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What I'm going to do.

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I'm going to use a string class and then use the method reference syntax.

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I'm going to perform some kind of operation on that.

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So what is the operation that I can do?

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Here I'm performing a uppercase operation.

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So the difference between this map and this map is that this map method is converting the whole type.

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But if you take a look at this map method, it is not converting the type.

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It is performing some kind of operation on the string input.

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So the output is again going to be a stream of string, but.

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It performs uppercase operation on each input.

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Right.

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Let's run this and check the output is going to have all the string with uppercase operation.

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There we go.

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So the result is a collection of names, but it has the uppercase operations performed on top of it.

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Now, I do not want the list.

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I want the set.

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How can we do that?

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There is a handy method which is available as part of the collectors here.

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What I'm going to do instead of this names list, it's going to be a names set.

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And in here, what we are going to do instead of the two list, we are going to use two set.

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Okay, so this is going to be set of string.

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And then let's import this.

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There we go.

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So we have to change this one also to set.

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So here we have changed the type of the collect method.

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So the collect method is going to collect a set of string, not the list of strings.

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Going to print that.

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Also, it's going to give me the same result, but the collection type is different.

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I'm just showing you the different types of collectors that we can use in order to achieve or in order

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to get your desired result.

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There you go.

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So I'm going to run this.

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It is again going to give you the same result.

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But the thing is, the first one is returning a type of list.

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The second one is returning a type of set.

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So this is all about map at the moment.

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There are a lot of other operations which we can perform, but for now we can stop with this and we're

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going to focus on some more methods of the stream operation in the next tutorial.

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With this, we came to the end of this tutorial.

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Thank you for watching.