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‫Welcome back to the polymorphism example.

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‫In this video, I'm going to use a different approach where you first of all have a little challenge.

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‫You should write some code which will help you to understand inheritance a bit further or a bit better.

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‫And then we will go into the poly forms, make part of this whole program.

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‫So please go ahead and try to write the code according to this challenge here.

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‫So pause the video and try.

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‫All right.

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‫I hope you tried it.

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‫So I'm going to create a new class ed class, and I'm going to call it car.

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‫And this class is just going to be a general car class.

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‫And it can contain or it should contain properties.

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‫Right.

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‫As I said, it should have a property called HP Prop and it should be an integer and HP is going to

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‫be the horsepower.

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‫So how powerful is this car?

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‫And then another property which is of type string and which is the color?

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‫Now what I need next is to have a constructor.

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‫So I'm going to create a public car which takes in the HP and the color.

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‫And here I just set this dot HP as the HP and this dot color as the color.

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‫So this color is going to be our property color and the HP is going to be the HP of our class or of

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‫our object that is created off type car.

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‫Now the next one should be the show details method.

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‫So public void show details.

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‫And in here we just write something onto the console.

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‫So CW, HP is going to be plus HP.

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‫Then we have the color, which should be something like the color.

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‫So of course I could use a different approach where I use string manipulation here, but I'm just going

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‫to keep it like this.

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‫Very simple.

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‫So the next one is a public void and it's called repair.

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‫And we're going to change those two methods later on.

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‫So no worries.

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‫But for now, I wanted to keep them very simple.

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‫With the approaches that we have used so far, that will make it more clear what polymorphism does and

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‫here just says car was repaired.

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‫All right, so that's our car and that's our base class.

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‫And now we need the two other classes, which is our BMW, BMW class.

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‫And in here, as I said, we have an additional property called model and this is a string model.

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‫Now, another aspect was the brand, which is a private member.

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‫So private string brand and it's called BMW.

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‫Now next we need a constructor, so a public BMW.

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‫And before I do that, before I create the constructor, I want to inherit from car.

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‫So now my BMW is going to inherit from car.

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‫And what I need here is the HPP, then the color

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‫and the model and here and comma.

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‫So what I can do is I can set the HPP to the HPP actually I can even go ahead and do the same with the

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‫color.

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‫It's going to be the color and the model which is our property should be the model.

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‫So this one here, there, I use this because I want it for this object and the same thing I can do

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‫here and I can do here.

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‫So even though I don't have created those in here, as you see, I can still use them.

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‫Now, here's something that you haven't seen yet, which is base.

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‫So I can use the base keyword here and then I can simply say, okay, I want to use the HPP and the

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‫color of my base class and then I don't need those two lines anymore so I can even get rid of those.

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‫As you can see now, the error disappears as well.

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‫So now we have created a constructor which uses the base constructor of our base, which means of our

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‫base class, which is our car.

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‫It's just going to use this constructor and it's just going to add the model.

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‫So now we have a very short constructor which does all the job, all the whole job.

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‫So now what I need next is a void show details, as I said.

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‫And in here I just want to show the details and I'm just going to copy the method from here or the entry

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‫of the method.

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‫And in here it's going to be the brand first.

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‫So brand plus brand plus HP.

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‫So now it's just going to show some additional details.

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‫And here, as you see, show details, hides, inherited member car show details, use the new keyword

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‫if hiding was intended.

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‫And that's something that we're going to cover in the next video.

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‫But for now, let's also create the repair method, public void repair.

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‫And in here it should just say something like the BMW

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‫and in here was repaired.

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‫So what is this zero that I have there?

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‫Well, that's the model.

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‫So I just want to know the model of the car and I'm just going to say, let's say BMW, Z, Phi, az4

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‫or MX three or MX five was repaired.

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‫So that's what this should do.

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‫And now I need another one, another class, which is pretty similar to what we have here.

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‫So I'm going to create a new class and I'm going to call it Audi.

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‫And for simplicity, I'm just going to copy most of the stuff here, actually, the whole class, because

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‫it's going to be very similar.

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‫What is different is here that it's an Audi and that we have the Audi as the constructor and of course

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‫it needs to inherit from car.

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‫So now that is done and now comes the polymorphism part.

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‫So we have an Audi which is of type car, we have a BMW which is also of type car.

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‫And we have this base class which is car, and now we can go ahead and create multiple objects of that.

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‫Now it will make a lot more sense as soon as we get there.

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‫So let's go ahead and create a new variable called cars, which is going to be a new list of cars.

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‫And even though this is a list of cars, so of the car class, we can create all these and BMW is in

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‫here.

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‫So just can create, let's say an Audi which is blue and is an A four.

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‫Then we have a new BMW which is, let's say 250 HP and let's say is a red car and it's an MX three.

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‫So that's one part of polymorphism that you can use the subclasses instead of the base class or the

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‫deriving classes instead of the base class when working, for example, with the lists or in general

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‫and by general, you will see what I mean.

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‫So what I'm going to I'm going to do is I'm going to run a for each loop, which is going to check all

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‫my cars in my cars list.

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‫And it's just going to write something like car repair or it's going to call a repair method.

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‫All right, so let's call that or let's run that.

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‫But before we do that, we need to console the right key.

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‫Because otherwise our program will simply close.

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‫So there you are.

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‫Car was repaired.

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‫So now it's calling the car method here.

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‫Which which is this one here?

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‫Car was repaired.

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‫So it's not calling this repair method and neither does it call this repair method, which was the BMW

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‫was repaired or here it's the actually here it should be audio or Audi.

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‫Audi was repaired.

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‫So now why does it call the repair method of our car and not the one of BMW and and the Audi one that

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‫is has to do with two things.

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‫So one of them is we have this void repair, which is not a virtual one.

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‫So if we make it virtual void repair, what we now can do is, for example, here we can override it.

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‫So now we can override the repair method.

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‫What that will do is if we run the code again.

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‫We will see.

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‫Car was repaired.

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‫That's our Audi, the first one.

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‫And then the BMW M three was repaired and that is the second one.

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‫And that is because our BMW class here has overridden the repair method.

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‫So we can simply take this method, make it virtual, and that allows us to override it in the deriving

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‫classes.

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‫And that's what we have done here.

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‫So now there are the two aspects of polymorphism.

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‫So polymorphism network one and ODI and VW, Porsche, whatever different classes you want to have can

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‫all be used wherever a car is expected.

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‫So whenever they are inheriting from this class here, from our car class here, this one, we can simply

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‫use it instead.

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‫And then the second aspect of polymorphism is that the virtual method can be invoked on each of the

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‫deriving classes, not on the base class.

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‫So that's something that we have done with the BMW and now we can do the same thing with our order here.

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‫So I'm just going to make that an override as well.

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‫Override, void, repair.

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‫Now let's run it again.

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‫And now both should show their brands and their models.

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‫So we see the Audi A4 and the BMW M3 were repaired.

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‫There is one more thing about polymorphism, though.

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‫So if you want to hide the base class members with new members, you can use the new keyword.

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‫So let's say we have this void show details method in our class car, which is just a void.

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‫It's not a virtual void.

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‫And now if I would like to override that, so not override in the sense that we have done here with

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‫the override one.

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‫But I actually want to use this method instead whenever I'm using a BMW and not in the sense of overriding

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‫the old one, but just hiding the one from car and using show details instead.

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‫I can use the new keyword.

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‫So what that will do is it will simply say, okay, this show details has priority over the car show

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‫details.

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‫So it's not overriding it, but it's reprioritizing it.

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‫So now how do I shoot?

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‫Show this show detail method or use this show method?

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‫Well, let's create a new BMW pmwz3, which is going to be a new BMW car with 200 horsepower.

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‫Let's make it black.

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‫And then it's az3 model.

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‫And then let's also create an Audi, Audi a three.

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‫It's going to be a new Audi with, let's say, 100 horsepower.

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‫And this one is green.

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‫Very weird color for a car.

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‫And then you have a three model here.

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‫Now, let's run the BMW and show details method here.

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‫And the same for the Audi.

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‫Audi.

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‫A three to show details.

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‫So let's just run that.

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‫And you see HP 200, color black HP 100 color green.

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‫So as you see, it's calling the car show details method and it's not calling the one from BMW.

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‫And that is because we have created it as a car, but it's a new BMW as a car.

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‫So if we do the same thing now, let's go ahead and create a BMW MX five, which is going to be not

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‫a car, but this time it's a B, M W new BMW and this one, let's say, has 330 horsepower.

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‫It's white and it's an MX five.

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‫So now if I call this B M W MX five dot show details method, it will show me the brand as well so that

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‫we are brand BMW, HP 330 color white.

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‫And the first ones.

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‫So those ones here.

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‫They also had to show detailed method, but they used the one of car and now the BMW one uses the one

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‫of BMW.

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‫So even though we said new BMW, we still use the car class in order to create a car object of of that

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‫which is internally a BMW, but we call the cars methods and not the BMW methods only if we go ahead

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‫and create it as a BMW we call the new method.

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‫So this new here, it simply says, okay, if you create an object of me, then go ahead and write it

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‫as new.

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‫If you don't, then go ahead and simply use the method of cars or of the car class with the base class

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‫pretty much.

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‫But what if I want to call the show details method of my base class onto my BMW object?

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‫Then I can do the following.

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‫I can go ahead and create a car which I'm going to call car B, it is going to be a BMW m five.

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‫But it's going to be.

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‫A car.

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‫So here I'm using casting so that I'm casting my BMW into a car and now I can go ahead and use the car

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‫b dot show details of my BMW MX five.

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‫Or of my car be so that we are once again hpp 330 colour white.

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‫So that's our BMW m five here.

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‫So why would you even use this approach of hiding and using this new keyword here onto your members?

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‫Well, you would use that if you want your derived member to have the same name as a member in a base

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‫class, but you do not want to it to participate in a virtual invocation.

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‫So that's when you use this new keyword that we have seen in here.

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‫Otherwise, if you want to override it, you can simply use this override approach here or this override

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‫keyword in your declaration of the method.

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‫All right.

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‫So that's quite something or polymorphism.

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‫In the next video, we are going to check out how we can prevent that.

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‫So if you don't want that a method can ever be overridden.

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‫There is a way to do that in our base class.

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‫So see you in the next video.