Inheritance

class Television {
  void turnOn() {
    _illuminateDisplay();
    _activateIrSensor();
  }
  // ···
}

class SmartTelevision extends Television {
  void turnOn() {
    super.turnOn();
    _bootNetworkInterface();
    _initializeMemory();
    _upgradeApps();
  }
  // ···
}

class Television {
  // ···
  set contrast(int value) {
    // ···
  }
}

class SmartTelevision extends Television {
  @override
  set contrast(num value) {
    // ···
  }
  // ···
}