main.dart

class Spacecraft {
  void describe() {
    print('hi');
  }
}

class MockSpaceship implements Spacecraft {
  @override
  void describe() {
    print('mock');
  }
}

abstract class Describable {
  // 抽象メソッド
  void describe();

  void describeWithEmphasis() {
    print('=========');
    describe();
    print('=========');
  }
}

class Describe extends Describable {
  @override
  void describe() {
    print('this class extends Describable class.');
  }
}

void main() {
  MockSpaceship().describe();
  Describe().describeWithEmphasis();
}