All language subtitles for 13. Polymorphism in Action

So we're on to our final pillar and that's polymorphism or changing shapes.
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How does this work?
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Let's say that we're abstracting our program and we're creating a separate module for separate roles.
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And we're inheriting a lot of the behavior from parent classes.
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But when we're doing a lot of inheritance, we know that we get basically a copy of what the parent class
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is able to do.
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So our electric car can drive and our electric car has the same properties. But we don't really want
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to end up with just a whole bunch of clones in our program. That isn't great
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right?
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We want to be able to define customer behavior as well.
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So in the case of our chef and our pastry chef,
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well, there's probably similarities between those two roles.
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They can probably both bake something in the oven and they can probably both make some sauce in a saucepan.
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But they might go about those behaviors a little bit differently.
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So maybe the pastry chef has to be a little bit more delicate with the things that he's working with,
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and the chef maybe,
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well she has to do things a little bit quicker because it's complete mayhem in the kitchen.
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But the point is that when you are inheriting from a parent class, there are probably things that will
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save yourself time that you don't have to recreate and you can simply inherit.
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But some of those behaviors that you inheriting, some of the methods, you might want to customize it for
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your own needs.
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There's two ways that you can do this.
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Continuing our car analogy, we might have simply a LevitatingCar, and this LevitatingCar is going to
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inherit from our Car class.
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So we're going to write extends the Car class, and this is because a levitating car probably also has 5
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seats, then it probably also looks pretty much the same as a car. It might share the same properties
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but a levitating car doesn't have wheels, at least in my mind.
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And instead, if we were to implement the drive functionality of a levitating car, it would probably be
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a little bit different. Because we're already inheriting from the Car class that has a drive method, if
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we want to use the same method, we have to override it and to do that we use the @ sign to specify
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that there's a very important word coming up, and the word is override. And then on the next line, we can
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create our own version of drive so we can write void drive and it looks exactly the same as before. But
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now, it's our own version of the drive method and our levitating car instead of moving wheels,
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it's going to simply glide forwards, very classy.
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So now when we create our levitating car,
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and we call upon our levitating car, our MagLev to drive, then you can see that it should now glide forwards
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instead of using its parents implementation of drive. So even though I inherit from my parents a number
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of traits and a number of behaviors, there's also things that I do differently from them or I'd like
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to think I do differently.
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For example the way I use a computer, I might get to use a computer to program it whereas my parents
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might just use it to go on Facebook.
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But the point is we are now able to override a parent behavior and provide our own custom version of
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it but we can actually go even further than that.
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We can actually take some of the good parts from our parent class, but simply just add to it.
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Let me show you what I mean.
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Let's build a new class and this is going to be a self driving car.
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And of course it's a car.
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So it's going to extend the car class.
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It's going to have a drive method and it's going to have 5 seats. So, easy. That was done.
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But in addition to being able to drive and make the wheels turn,
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I also want my self-driving car to be able to steer the car as well. Instead of simply just getting the
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wheels to turn,
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I'm going to get my self-driving car to drive me towards a destination.
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So I'm going to create a new property called destination. And this destination is going to be set when
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I create a new object from the self-driving car.
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So I'm going to define a custom constructor, so self-driving car, when we create it,
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we have to provide a destination. And we'll call that userSetDestination.
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And then once we create our self-driving car, we'll set the destination property to equal the user set
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destination that was provided when we created our new object.
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Now inside this self-driving car, when we decide to drive it, we kind of want to inherit the functionality
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of driving which is wheels moving,
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and as a consequence the car moving.
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But we want to add to it as well. We can again override our parent method code drive.
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So it has to look exactly the same.
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It's also void drive empty parentheses.
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And then we're going to trigger the parent behavior by calling super, which stands for the superclass
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or the parent.drive.
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This is going to carry out the behavior of the superclass' drive method.
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But then afterwards, we're going to do our own thing. We're going to say that the steering is going to
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steer us towards the destination.
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Here's how it would look when we actually call this method in our main. So we could create our new self
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driving car, we'll call it myWaymo. And it's gonna be equal to a new self driving car. And when I create
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myWaymo as a new self-driving car, I have to provide a destination.
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So let's drive it towards 1 Hacker way.
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And now when I say myWaymo.drive calling that drive method,
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then when I hit run, you'll see two things happen.
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One is that it'll carry out the parents version of drive, which is simply to print 'wheels turn', but it'll
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also do its own thing which is steering towards the destination.
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And this all comes from just calling that one drive method.
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This is polymorphism in action.
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We're able to inherit from our parents, but we're able to also improve on it.
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We're able to change it be a little bit different by overriding their methods. And if we come back to
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our Flutter code, you can see that we're doing that every time we're calling the build method.
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So a stateless widget already has an implementation for the build method, but in our code, we override
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it and we provide what it is that we want to do instead.
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And this way, even though we're inheriting, we're able to be a little bit different and customize what
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our stateless or our stateful widgets do.
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So getting the best parts, but then also doing custom things using these inherited classes.