Programming in Dart: Classes

Jun 28 2022 · Dart 2.17, Flutter 3.0, DartPad

Part 2: Learn Inheritance

15. Use Abstract Classes

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Previous episode: 14. Challenge: Override a Method Next episode: 16. Implement an Interface

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So far, things have been straightforward but with this episode, things are about to get a little abstract. I’m going to introduce you to abstract classes. But before we discuss abstract classes you need to understand the concept of an interface.

ImageGenerator generator = NetworkGenerator();
generator.fetchImage();

abstract class HelloWorld {

}

var hello = HelloWorld();

var message = 'Hello World!';

String getHelloString();

class BackwardsHello extends HelloWorld {

}

@override

String getHelloString() {
    return message.split('').reversed.join();
}

class ShoutyHello extends HelloWorld {
  @override
  String getHelloString() {
    return message.toUpperCase();
  }
}

HelloWorld hello = BackwardsHello();

print(hello.getHelloString());

hello = ShoutyHello();
print(hello.getHelloString());