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Welcome back.

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And this video I would like to cover inheritance and inheritance is one of the main concepts of object

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oriented programming, and it allows a class to inherit features such as properties and methods from

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another class and reduce them.

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So the structure is the following you have a subclass and then you have a super class.

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Alternatively, you can call the subclass child class or derive class, and the super class can be called

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parent class or base class.

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Now let's have a look at those in action, so let's create a new class called vehicle.

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Now, this class might have some properties and some methods.

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OK, and now we can go ahead and take this class and inherit from it.

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So this means that we will take its properties and methods and we will make them reusable.

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So let's go ahead and create a new class called car, which is of type of vehicle which inherits from

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vehicle.

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If you do that, you need to make this class open, so vehicle needs to be an open class.

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Otherwise, I cannot use inheritance here.

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And that is because all classes in Courtland are final by default, which means they are non inheritable

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by default.

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So you need to use the open keyword to make a class inheritable, and that's what we're doing here.

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So we're using open class vehicle.

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Now, let's say I want to have another class which inherits from car, so class electric car that should

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inherit from car.

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Now problem is car is not open, so I would need to make it open as well.

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All right, so if you want to make sure that a class cannot be inherited, you can use a sealed key

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word, then this would not work.

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So you cannot inherit from a sealed class and you can even see that converts your subclass to an object.

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And I'm just going to get rid of that because I want to make it open so that we can reuse it.

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Now, this year, our vehicle is the superclass or parent class or base class, so you can use either

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of those terms.

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Each of them is fine.

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Now, this year, our car is the subclass of the vehicle class.

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And of course, it's also not just a subclass, but also the child or derived class.

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OK, so it's just different terms, but whenever you come across those terms, you should know what

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they are, right?

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And then at the same time, our car is to superclass parent class based class of vehicle.

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And of course, in that case, the electric car is the surplus or childless or derived class of the

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car class.

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OK.

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So.

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Let's get rid of vehicle now because I want to only work with car and electric car for now.

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So let's say we have some properties in here and let's also say that our car has a primary constructor,

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so we want to have some more value in here.

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Well, name will be a string value brand will also be a string.

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So this car has a name and they brand.

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And then here, electric car, suddenly we have an error here, so we need to add a constructor parameter

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name.

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As you can see here, name is now required and something else is missing.

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The constructor parameter Brent is missing.

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So you can see.

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This is how Courtney expects it.

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So you need then to use the same parameters that were used for the car, for your electric car as well.

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So there's just a constructor that we're using here, the primary constructor.

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Now, of course, the electric car can be extended, so you can add more features to it.

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It has to have at least two features of the class that it inherits from, but it can extend features

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so it can have additional features such as, for example, battery life.

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So an electric car would have battery life, which is of type, let's say double.

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So that is the base structure when working with constructors.

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So with primary constructors.

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Now, let's say we have a ranger here in our car, so let's create this class car first here range.

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It's going to be of type double and it's going to have a value of 0.0 just as an example here.

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Then it has a function in here fun extend range, which will be the amount which will be of type double.

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And if the amount is positive.

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So great zero.

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Then I want to increase the range by the amount.

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OK, so if we.

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Go to the fuel station and we fuel up our car and the range will be extended, so we extended the range.

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And then finally, I want to have another function here fun drive.

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So distance should be double.

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And I will just print here drove for distance kilometers.

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OK, now I have this class car and of course, our electric car inherits from it, so that means that

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if we now go ahead and create a fund main, so our main function and in here I create an object off

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car.

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So far, my car is type car.

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Now, of course, I need to add a string, so I'm going to give it the name, for example, A3, which

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is of the brand already.

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And then I create a electric car, so my car, so I'm going to call it, is going to be an electric

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car.

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And here it's going to be Tesla S or maybe s model of type Tesla.

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And then it of course, needs also to have a battery life.

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So I'm going to give it 85.0, which means 85 kilowatt hours.

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All right, and the cool thing now is let's go ahead and use my car, don't drive.

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And we will see that it needs a distance, so let's say drive for 200 kilometers and here, of course,

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it's a double so 200 to two.

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And now let's do the same thing with my car that drive and use also two hundred kilometers.

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All right, so if we run that now concede it doesn't complain, even though there is no drive method

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inside of my electric car, there's actually nothing in mind extra car class.

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It's using nothing.

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The only thing it does is it inherits from the car class.

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So let's run it and test what the result will be.

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And we can see that it says drove for 200 kilometers and drove for 200 kilometers.

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So in both cases, it drove for 200 kilometers, even though electric car never implemented a function

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called drive.

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All right.

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But it can still use it because it extends the functionality of its parent class, so it has all of

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the features of its parent plus.

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It was also this feature called Extend, so we can also go ahead.

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Maybe we should rename those.

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So that's going to be the Tesla S and Audi A3.

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And let's reuse those names because I think it's more telling to use those names.

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Now you can see that our Tesla can drive for 200, but our Audi can also drive for 200.

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Now let's extend our duration or the range of our Teslas.

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So Tesla is not.

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Concede has extended range does name range brand to try to string all of those, so it has several.

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Functions which we have never created, for example, hash code equals and to string.

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And these are the ones that are always available.

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These are always available.

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Why are they always available?

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Because any class inherits from the any.

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Class, so I say it again.

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Any class inherits from the any class.

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So there's a class called any, and we can use this type any as we've seen before.

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So for example, I can create an object bar object.

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One is of type any.

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Okay, so and he's a class in Scotland.

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Let's see it.

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It's an open class, the route of Scotland class hierarchy.

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Every Scotland class has any.

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As a superclass.

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And that's why we can always use the function or the method equals hash code and to string.

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And can overwrite them as well, we can create our own types of those.

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But now let's go back and use the extend range here.

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So let's extend the range by 200.

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So now we extended.

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The potential distance that our Tesla last can drive by 200 kilometers.

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And that is because we have this fun extend range in our car class.

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Now let's go ahead and let's say we want to override the range functionality and we want to override

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the drive functionality.

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So what we can do in our class electric car, we can just go ahead and say override bar range is battery

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life multiplied with six?

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So let's say with 85 watt hours and we can drive something around five hundred and ten kilometers or

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so with this range.

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So it's more or less realistic.

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I think maybe it's just five, but something around that five or six times the battery life in kilowatt

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hours is what a Tesla can drive.

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So now we are overriding the range property.

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Now, of course, it's complaining.

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It says, OK, you cannot override range because the range is not open, so you can make.

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A property open as well.

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So here we can use open for this property called the ranch.

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We can use the same feature for a function.

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So now we made this drive function open as well.

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So now we can go ahead and overwrite that functionality so we can say, for example, in our electric

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car, that we.

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Drove his override, fun drive, and we say we drove a certain distance, but we also print line.

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Say something like drove distance on electricity, but that by itself wouldn't be as interesting as

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doing the following so we can confuse the whole thing.

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Let's go ahead and say drive.

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And now we just print something like drove range kilometers on electricity.

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So now what we have is we have a drive function, which we override from our parent class and we have

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a drive function, which we created inside of our inheritance.

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Which we created inside of our subclass.

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This might not always be a good idea, because it might end up being confusing, but in the end, now

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you can go ahead and say Tesla start drive.

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And you can see you have two options here, so you can either drive or you can drive a distance.

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So let's say we drive.

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So before we used to distance feature and now we just drive because we want to know how far a Tesla

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can drive and if we run that again, then we should be able to see the maximum range of our Tesla S.

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And we can see that we get 710 kilometers on electricity here.

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So we have created an overriding function, so we are overriding the functionality of our superclass,

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so it would change whatever was written in here.

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And then we create another function, which is now specific to our electric car, which has the same

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name, but it uses different features.

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Of course, we can have a bunch of other variables in here as well, so we cannot just have the variables

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that are used in our.

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Superclass here for the electric car, but we can also have a charger type, for example, let's say

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different electric cars have different charger types or something like that than we can say, Okay,

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this car has a charger type of one.

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And if you want to change dad, we can of course do so for every single Tesla s that.

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Charger type, and let's say it has a type two charger.

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All right, and there's one thing that I should say that what we're doing here with these two.

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So let me put that a little further down.

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What we're doing here is called poly more, because at least that's part of polymorphism.

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Polymorphism is the ability to treat objects with similar traits in a common way, which we are doing

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right here because a Tesla has common traits, because it's inheriting or it's of type electric car

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and it's inheriting from car.

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And this, of course, only works because electric car is a subclass of car that would alternatively

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also work if it was a subclass of car, which was an interface.

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OK, so if car was an interface, that would work as well.

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But what interfaces are is something that we're going to look at in another lecture.

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All right, so that was a little introduction into inheritance, and let's see some more examples of

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that, for example, with interfaces and the next video.