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Inheritance is one of those fundamental aspects of object oriented programming.

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It means classes can inherit properties or functions from superclasses.

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It means one class can become a base class for somebody else.

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Now the good news is you have actually been using inheritance for the most part of everything we have

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been doing.

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But now in this lesson I'm actually going to make my own classes and then have a parent child relationship

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between them.

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That's how we can do that.

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I'm going to go to school and start a new project and I'm going to call it inheritance science street.

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So here is how what I want to do and how I'm going to do it I'm going to write it down first I'm going

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to have a class of vehicles and then my class because I'm assuming this the vehicles that they go on

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land essentially.

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Now I'm going to say that has a subclass called sedans.

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All right so I have the Waco's class and from there we have the seeding classes and then begin to learn

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how to override functions.

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And then we're going to learn how to add new functions and all that's pretty much most of for the really

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matters.

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So let's go ahead and get started.

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I have a class called Veeck.

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And it doesn't have a superclass.

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What it does have is this it has a variable called tires and that's an integer.

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Explicitly wrapped optional that it must be there.

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So my vehicle has a number of tires.

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How many tires are there.

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And then I'm going to go ahead and say it has an in it in tires and there's going to be an integer because

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you can imagine make self tires be calm in types.

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I'm actually going to go ahead and add one more function of my own as that I'm going to call it.

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Charlie vate.

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Let's call it an integer input rate.

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So essentially of the other reference I am writing in in an X and Objective-C so input rate which is

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going to be an integer.

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Right.

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So I have that and the return is actually a boolean.

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So whether this is going to be possible or not and I'm going to say by default the carry rate actually

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returns false.

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Unless our vehicle can carry something so let's see how we're going to subclassed these and how are

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we going to inherit this stuff from it.

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Let me clear things up so we can actually you know write more code in here.

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So the next class I have is a class of sedans so I'm going to say class now when I'm defining my sedan

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class I'm telling myself well every seat on is kind of a vehicle.

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It has to have a certain number of tires and it can carry a certain amount of weight.

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It might have an interest in it that initializes a certain number of tires.

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So what if I say my sedan is actually a child of vehicles or you could read it in a way that CNN has

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a base class called vehicle or vehicle is the superclass of Sedan.

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So that's about that.

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I have this now and I have a class called sedan and if I wanted to I could actually go ahead and use

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it.

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Let me again get myself a little bit more space and I'm going to use it for you.

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I'm going to say let me bring this one down.

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OK.

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All right so now I'm going to go ahead and say let's call it what's a C Now let's say Ford Fusion for

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the fusion.

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That's a sin.

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I hope so.

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It's a sedan.

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And the only type of it that it has is the input of number of tires they say well it has four tires.

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So now my sedan class is essentially the same class as vehicle.

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It's exactly the same thing.

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But what have see now I have a variable called sunroof and that would be a boolean value.

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And that's the specific to see whether they have sun roof or not.

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And now as you can imagine in Ford Fusion I could go ahead and say some truth is for instance true.

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This same wasn't valid for something that is made of the type we cause.

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In theory I could go ahead in here and say my Ford Fusion is a vehicle with input tires for.

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But then this one is going to give us an Aero is going to say so what is sunroof in here exactly.

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Because a vehicle doesn't have a memory card sort of.

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So so far we managed to have a class that borrows some of stuff from its parents class C Don borrows

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from bacon and adds its own set of parameters and attributes.

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Siddhant and also have its own in it.

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So for instance I'm going to see on every seat on has a number of tires which is four.

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So I'm going to go ahead and say it him Sundra of sun roof which is a boolean value and then you say

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the body of my knee I'm gonna say the first thing is I have to initialize this.

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Based on its superclass.

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So I'm going to say super dots in it and say well what's the number of the tires.

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And let's say the number of those is always four.

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So whenever I see is being shallows that's going to be for and then I'm going to say self son who is

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going to be in put some of.

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So now we have a new unit for RCA Don that does initialize or object based on a sound off and we can

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use that.

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I'm going to go in here and say sit down in put some growth through.

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Well I don't need that line anymore.

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So what happened so far.

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We have a base class the base class has its own initialiser.

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It has a variable in there and we have a child's class or a sub class and subclass has a new property

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or a new attribute.

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I has a new in it.

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Now here's another thing a very common situation that happens sometimes you want to overwrite an existing

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in it.

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So how do you do that.

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I'm you're on say override in it and it says well you're trying to override it.

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This one.

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Yes that's the one I'm going to do.

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And where are you going to go.

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I'm going to say super DOD in it put the same value in them.

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All right.

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Or if you want manually pull put forward which kind of renders this one moot.

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Now the next thing I'm going to do is I'm going to say Songdo is Fox so by default whenever I override

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this in it and when I get the sunroof to be favs and that's overwriting and initialiser from our superclass.

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Imagine if you're initialiser you have to do something different than you or our parents class and that's

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something you override the initialiser you could of course overwrite an existing function.

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I could go in here and say as you can imagine there is no order between the methods of just writing

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in here so it's easier to zoom in to the screen and what to say overwrite function and the function

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I want to override is this guy.

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So not in this.

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All right.

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I'm going to say well it doesn't always return false if a simple rate is below 2000 than our return

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through else let me put the else over there as well.

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I'm trying to be more economical with my space illustrator and false of course.

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So that's about you know overriding a function.

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So that's pretty much the basics of inheritance.

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You have a class that class has some stuff in it you subclass it to another one and that one can add

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on a stuff overwrite functions from parent class override units from power Pyne's class have its own

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specific in it such as this one and work essentially independently.

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Something you might be wondering is so one why would we use this.

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When do we use a situation like this.

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Almost entirely always.

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And that's the principle of object oriented programming trying to modularize your code.

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So it is essentially easier to write and to read.

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So if I'm writing an application let's forget about the cause and see what happens and what not.

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Let's imagine I'm writing an application that say real estate listing application.

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You have multiple different types of states right.

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So for instance you have listings that are for sale you have listed that are for rental and then you

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have listening that are residential and then you have these things that are commercial and then you

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have less things that are in the city.

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All right.

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And then you have these things that are perhaps you know out of a state or whatever that you are trying

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to do.

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There are lot of different things that are common between all of these things.

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So in a situation like this I would go ahead and say class property and then subclass sale and then

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from subclass of state I would get something called residential.

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Let's quickly demonstrate say that I'm going to say costis call it property and this is a class that

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has the building blocks of a listing that you know you can have your app and then on that I have a class

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and that class is going to be sale.

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And that's a subclass of property property.

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And then I'm going to have another class that's going to be residential and that superclass of that

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is going to be saved.

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So it's essentially a hierarchy of different objects that they inherit from each other.

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Every one is a property.

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Everyone is for sale.

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So let's imagine everyone has something called price.

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Right.

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So price is an integer value for instance.

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So everybody has a price.

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And then the ones that are for sale.

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They also have availability for instance.

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So let's go ahead and say Vire Let's see.

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And that's going to be a date right.

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And then the ones that are residential are for instance they have something called variable number of

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or just rooms.

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All right which is a number of the rooms that are available you know residential for sale property so

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on and so forth you know all of these things they essentially trickle down.

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They go from one to another to another and that's you that's how your code becomes more and more modularized

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and easier to read and easier to understand.

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We will see a lot of these kind of things in the coming you know examples on the actual apps that we

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make.

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We try to subclass as much as we can.

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Another thing that you know you often end up doing is subclassing something that already exists.

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Phrase as I want to get a class called my a string to be a subclass of the string because I want to

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add an extra function to it.

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I want something to happen in here which Genesys thing doesn't do it by default.

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That's all I'm working on an app that has to I don't know who to to reverse every listing that I give

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it to.

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I give to him and I want to have the built in feature of this thing so I can just going here on a new

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class that inherits everything from a string but also has some extra stuff in it.

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And we will see more of this when we talk about class categories and class methods as well.

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For now if you have a class this is how you stop classes this is how you inherit from that one you are

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good on the stuff you overwrite functions and you use them independently.

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That's about that.

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And let's move on to our next guest.