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 explore the flatMap method that is part of the optional class.

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The first step which I'm going to do is that I'm going to introduce a new class called Bike.

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New class called Bike.

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And this is going to have.

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Private string name and model name and model.

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And we are going to generate.

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The getters and setters for this one.

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In red.

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Select all the properties and click okay.

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And then I'm going to generate the two string method to.

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There you go.

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So we have the bike object.

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Sorry, the bike class created.

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Now I'm going to build a relationship between the bike class and the student class.

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If you take a look at the student class, we are going to incorporate bike in here.

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So the use cases, not all the students will have the bike.

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So the students, whoever has a bike, will use their bike to come to the school.

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How can we represent that?

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So this is going to be an optional property because not all the students is going to have the bike.

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How can we represent that using optional so private optional of bike and just give it a name.

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This is going to be by default optional dot empty.

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So as a developer, just by looking at this model, which is the student class, I can say, okay,

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I have an optional object which represent this is not a mandatory property that each and every student

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will have.

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Right now.

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Let's go ahead and generate the getter and setter method for this.

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Rate getter and setter.

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Okay.

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And then let's read the two string also.

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Replace the existing two string method, Click on.

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Yes, there you go.

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And what I'm going to do, as you mentioned, not all the students are going to have this rate at the

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bike.

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I'm just going to add it to student one or what I can do.

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I can have this added just to the supplier bike, bike equal to new bike, and then the bike is going

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to have a name and model.

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So set name equal to ABC and model equal to.

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Let model equal to x, y, z.

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So what I'm going to do, I'm going to create a student instance and then return it.

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Student Equal to and then Student Dot set bike equal to going to be optional.

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Dot off.

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Nullable.

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Bike and then return this shirt.

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So now we added the supplier method, right?

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So we added the supplier method in the supplier student supplier.

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We added this bike optional to the student object and we are returning that as part of this supplier.

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Now let's go ahead and code this.

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Using the optional bike.

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So what is the scenario that we are going to code?

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We are going to code the flat map example.

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Let me put this in presentation mode.

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In here, what I'm going to do, I'm going to create public static.

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Going to be.

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flatMap.

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Right.

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Optional.

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flatMap.

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And then I'm going to call similar code.

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So this is going to give me the it's going to be a wide method.

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This is going to give me the optional object back.

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Right.

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So now my use case is I want to get to the bike name.

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I want to get to the bike name and print that bike name as an output.

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That's what I want to do.

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How do I get to it?

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The first thing I'm going to call student optional and then I'm going to have the filter method to filter

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the student, the student GPA.

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Is greater than 3.5 then only greater than or equal to 3.5.

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Then only I want to get to the bike name.

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And then.

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So what is the type of bike name in the student class?

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The type is of type optional, right?

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So in order to get to the optional object inside an optional object, because it's already an optional

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object, you want to get to the optional object which is inside another optional object.

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The only way to get into it is by using flatMap.

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So if you remember for the streams API we have used the flatmap.

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flatMap is used to flatten the stream which represents multiple elements actually.

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So let's say you have a list of elements inside a object.

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Then in those kind of scenarios, if you want to flatten that stream to each and every element to represent

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a stream, then we have used flatMap in that example.

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Now we are going to use flatMap in the optional context.

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So in the optional context, flatMap is used to get to the actual value of the optional object inside

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another optional object.

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Dot get bike.

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And we're going to map that to.

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Pike dot get name.

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This is what we want, right?

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And then this is going to return a student.

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It is going to return us string name and it's going going to be of type optional.

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Was a map again and optional is going to return another optional right here.

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It encapsulates the name as a the bike name inside the optional.

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Object.

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So here we are going to call this method and this is going to print the bike name.

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Let's go ahead and execute this program.

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If we executed it gave you the optional ABC.

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You want to get to the name of it?

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We'll do the If percent.

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Name Dot if present then.

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We are going to print it right now.

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Yes, you can give a different value here.

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Name is.

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Yes.

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Let's run this.

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Run.

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Thus it gave you the name as ABC.

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Okay, let's go through this pipeline again.

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So what happens in this line?

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In this line, this is going to still return optional of shouldn't.

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Now we have to access the bike which is inside.

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If we take a look at it, the bike will be inside this as an another optional object.

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Right.

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If you want to get to the access, you want to want to get to the actual bike, you need to perform

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the flatMap.

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This is going to give you the optional of bike as a output.

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That's what it is going to do, but it needs to get into the student object first, which is of type

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optional and then get to the bike optional object.

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So that's the reason why we need flatMap here.

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And this gives optional bike as an output and using that we are mapping and getting the name of that

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and returning that as an optional of string.

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So this is what happens behind the strings.

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So here we have a two levels of optionals that's the reason why we need to have the flatMap.

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So here this returns the optional of bike as an output at this step.

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I hope the concepts are clear.

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So this is all about flatMap.

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

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Thank you for watching.