All language subtitles for 12. Inheritance in Action

Now that we've already talked about abstraction and encapsulation and seen it in action, let's move on
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to the next pillar of OOP which is inheritance. And inheritance,
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we're talking about it in programming refers to when a class is able to inherit properties and methods
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from their parents.
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So you for example might have inherited your eye color from your parents or you might have inherited
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certain behaviors like you are a neat freak and you really really need to keep everything super tidy.
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You might have gotten that from your mom or your dad.
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Similarly all classes can inherit from a superclass or a parent class and it can inherit properties
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as well as methods.
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And this is important because when we're abstracting our program and we're creating lots of different
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modules lots of different components that all take care of a specific task.
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It's likely that we will have some duplication in their functionality.
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So for example our pastry chef and our chef will probably have some similar functionality.
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They probably both know how to boil some water.
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They both probably have a method for baking something but they might do it slightly differently.
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So in order to prevent having to rewrite lots of code when we're abstracting into lots of different
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classes and separate modules, this is why inheritance is really key when you're creating objects. To demo
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this,
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I'm gonna go into a empty DartPad and I'm going to create a new class.
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Let's say that I create a Car class and my Car class is going to have some properties.
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Every car probably starts out with a number of seats property right?
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And we're gonna set it to 5 as the default.
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Every car I build is going to start out with 5 seats.
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Seems pretty standard.
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And then every car is also going to have a drive method because otherwise, why have a car
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If it doesn't? And when you call the drive method, it simply just turns the wheels.
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So I'm going to create a print statement that says the 'wheels turn'. And now when I create my car object
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from my Car class,
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so let's create a new car. Let's call it myNormalCar because a little bit later on, we're going to obviously
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make this a lot more souped up. So myNormalCar is just going to be created from the bog standard car
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class.
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So when I print myNormalCar
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.numberOfSeats for example, then you can see that I get 5. And when I say myNormalCar.
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drive, then it will try and perform the drive functionality and the wheels start turning.
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That's all pretty standard and we're familiar with how classes objects work in this way now.
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But what if I wanted to create a different type of car?
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What if I wanted to create an electric car?
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Well an electric car is kind of similar to a car right?
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It probably also has five seats and it probably can drive as well, but it might have some other functionality.
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Let's go ahead and create a new class and this class is going to be our ElectricCar.
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But I don't really want to have to type out all of this again.
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It's just the same as a normal car.
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But I want to focus my time on explaining how it's different from a normal car.
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So how can I inherit all of the things I get in car?
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Well in Dart, the keyword is extends.
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So my electric car is going to extend my Car class.
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And what this means is that my ElectricCarr by default, is going to have everything that a car has.
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So I could go ahead and create a new electric car.
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Let's call it myTesla and let's create it as a new electric car. And now I can straight up just say
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myTesla.drive and you'll see that it'll make the wheels turn.
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Let's go ahead and comment out the previous ones that we had related to our car so we're not getting
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confused in the console, and you can see this myTesla drive triggers that electric car to turn its wheels
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because it inherited all of that capability from its parent class, the Car class, and it also has a starting
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default number of seats.
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But by inheriting from the Car class, it means I don't have to repeat myself and type out everything
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that is common to cause an electric cars and I can just focus my time on creating code that is different.
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For example my electric car might have a battery level and it's going to start out at 100%. But
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when it goes down, I can recharge my electric car so I can have a method called recharge.
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And this will reset the battery level to 100%
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so now not only does my Tesla drive, it also can recharge
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and I didn't have to repeat the things that a car already has.
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I've managed to incorporate the properties and methods simply by using that extend keyword.
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This is how inheritance works and we can see this in our code as well.
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Every single time that we've created a new stateful widget or stateless widget, we haven't have to
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create all the properties or the functionality of a stateless or stateful widget.
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We've simply been able to tap into it by creating a class that extends the parent class a stateful
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or stateless widget.
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And if you hold down COMMAND or CONTROL on Windows and you click on that class, you can see that it has
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various properties and methods that we've been able to simply use because we're extending it. We're
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inheriting from it and all we have to do is to describe all the things are different from the parent
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class and focus on building out our custom functionality rather than on the basic boring things such
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as how do we draw a widget on screen?
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How do we give it a different color?
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How do we change its shape and size?
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How do we actually move the pixels around?
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That's all sorted out for you by the Flutter SDK and all of that capability are packaged into these
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parent widgets that we're able to inherit from. Now in the next lesson,
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I want to talk a little bit about the last pillar which is polymorphism.
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So for all of that and more, I'll see you on the next lesson.