headphone.dart

class Headphone {
  double volume = 5;

  void increaseVolume() {
    if (volume == 10) {
      print('최고 볼륨입니다!');
      return;
    }

    volume++;
  }

  void decreaseVolume() {
    if (volume == 0) {
      print('최저 볼륨입니다!');
      return;
    }

    volume++;
  }
}

class BluetoothHeadphone extends Headphone {
  bool isPlaying = false;

  void togglePlay() {
    isPlaying = !isPlaying;
  }
}

class NoiseCancellingHeadphone extends BluetoothHeadphone {
  bool noiseCancellingEnabled = false;

  void toggleNoiseCancelling() {
    noiseCancellingEnabled = !noiseCancellingEnabled;
  }
}

void main() {
  BluetoothHeadphone bluetoothHeadphone = BluetoothHeadphone();
  bluetoothHeadphone.increaseVolume();
  print(bluetoothHeadphone.volume); // 6

  bluetoothHeadphone.togglePlay();
  print(bluetoothHeadphone.isPlaying); // false

  NoiseCancellingHeadphone noiseCancellingHeadphone =
      NoiseCancellingHeadphone();
  noiseCancellingHeadphone.decreaseVolume();
  print(noiseCancellingHeadphone.volume); // 4

  noiseCancellingHeadphone.togglePlay();
  print(noiseCancellingHeadphone.isPlaying); // true

  noiseCancellingHeadphone.toggleNoiseCancelling();
  print(noiseCancellingHeadphone.noiseCancellingEnabled); // true
}