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 the classic stream map Reduce pattern using the streams API.

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The first step.

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What I'm going to do, I'm going to create a class called Dream Map.

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Reduce example class, and then I'm going to make this class executable.

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So in order to explain this use case, what I'm going to do, I'm going to add one additional parameter

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for our student object in the student class.

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What I'm going to do, I'm going to add a new attribute called private int notebooks.

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So this attribute, meaning this property represents how many notebooks each in every individual meaning

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each and every student has.

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I'm going to generate a constructor with all these values.

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I'm going to press Command N in Mac.

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In the case of Windows, you can right click and then you get this option right click and then click

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on Generate.

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It will give you this option.

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I'm going to click on constructor.

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Basically, I'm going to add notebooks also as part of the constructor so that it will be easy to build

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objects out of it.

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There you go.

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I have the notebooks that got added here.

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The next step is I'm going to update the student database with those values.

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Right now, we just have this.

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What I'm going to do, I'm going to add some random numbers to it.

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11.

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And then.

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Well.

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Here for this student, I can add ten.

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But the student again had zero nine for the student.

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I can add like.

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And for this student, we are going to add, I believe I should not.

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Zero for the student.

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It's going to be 14.

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So all these numbers represent how many number of notebooks each and every student has.

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The use case that we are going to code here is that what is the total number of notebooks that this

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whole collection has?

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Meaning What is the total number of perform the summation of all the notebooks that each and every student

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has.

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That's what we are going to code as part of this use case.

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Now let me put this in presentation mode.

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I'm going to create a method called private static int.

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Number of.

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Notebooks.

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That's what we are going to do.

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The next step is I'm going to get all the students from the student database, student database, dot,

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get all students.

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That's good.

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And the next step is we are going to map.

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That's the next step which we are going to do.

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But before that we need to call the stream method.

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Dream.

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Here we go.

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We have to map all the notebooks, right?

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Meaning we need to get this number.

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Then only we will be able to perform the summation on it.

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So what we do for that is that we'll call the map method.

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And then.

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So this stream is going to return us.

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Dream of student.

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And the next step is we are going to perform Student Colon.

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Colon.

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We are going to use the method reference syntax, and then we are trying to access the number of notebooks.

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And one more interesting thing is we did not generate the getter and setter method.

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That's the reason why we are not able to access it and it is of scope private.

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Now what I'm going to do, I'm going to generate getters and setters.

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There you go.

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The getters and setters are there.

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Now let's try to use that.

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Let's see whether do we have that recommendation for that?

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Get number of notebooks.

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There we go.

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We have the get number of notebooks, which is going to give you the access to the notebooks value.

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So what this is going to do, this is going to create the.

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Dream of integer.

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That's what it is going to do.

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What is the next step?

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So we are going to code the classic stream MapReduce.

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Now we start the stream and then we perform the map operation.

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Next is a reduce operation.

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The reduce operation is going to perform the summation of all the values in the stream.

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How can we achieve that?

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The way to do it is by passing zero.

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Let's keep that one as an initial value.

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Here, we can use the zero as an initial value because we are performing the summation, right?

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So summation, it is not going to change the result to zero because it is going to add zero plus whatever

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value that the stream is going to pass.

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And the next step is we all know it's an accumulator we are going to pass.

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It is going to take two values A and B and then perform A plus B.

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Right?

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Yep.

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That is good.

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Now, this is going to give us the result.

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And number of.

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Notebooks.

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Great.

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And then what we will do, we will return this.

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The number of notebooks.

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The next step is let's print this value, let's call this method and then check.

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A number of notebooks.

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Going to be.

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And call this method.

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Run this example and then check.

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There you go.

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What is the result?

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The result it gave is 71.

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Now I'm going to show you an alternative approach to perform this.

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If you remember, we have this integer class, which is part of the.

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Java.

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Itself, which comes with the Java Library itself.

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Integer, Colon.

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Colon.

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There you go.

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You have this max method.

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You have this sum method.

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You can use the sum method.

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This is going to perform the summation for you.

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So this is as similar to this operation.

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Let's run this and check.

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So the result that it returned previously was 71.

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Now let's run and check whether is it returning the same result.

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There you go.

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It printed the result as 71.

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So this is one another way of performing the summation.

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But if you take a look at the integer class, it doesn't have anything like multiplication.

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Right.

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So for those kind of use cases, we still have to implement the reduce function by our own customized

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pattern.

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Okay, So now let's go ahead and enhance this use case.

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Let's say I want one only the students who are in the third or fourth grade to have I mean, I want

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the students number of notebooks collection for the students who have the grade level as three and above.

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So in order to perform that, what I can do is I can add a filter.

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So it's so handy, right?

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So student.

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Student dot get grade level.

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Its grade level greater than or equal to three.

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So this is going to give you all the students whose grade level is greater than or equal to three,

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and then that is going to perform.

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So how many number of notebooks the students who are present, who are sitting in the grade three and

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four, It is going to give you the summation of all those notebooks.

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There you go.

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The number is 48.

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Let's say you want to add one more filter.

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So I want to just perform Student whose gender is female.

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Dot get.

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Gender dot equals.

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Remove.

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If you go to the students database class, it has the gender as male and female.

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I just want to know how many notebooks.

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Of the students who were in a grade level greater than or equal to three and their gender is female.

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On this example, we take a look at it.

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Result is 24.

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Result is 25.

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So this is one famous pattern of implementing the map filter and reduce example.

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With this.

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We came to the end of this tutorial.

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Thank you for watching.