thonglinhma

abstract class PlanetVisitor {
  void visit({Planet planet});
}

abstract class Planet {
  void accept({PlanetVisitor visitor});
}

class MoonJedah extends Planet {
  @override

thonglinhma

abstract class PrintStrategy {
  String print(String string);
}

class Printer {
  PrintStrategy _strategy;
  Printer({PrintStrategy strategy}) : _strategy = strategy;

  String print(String string) {
    return _strategy.print(string);

thonglinhma

abstract class State {
  bool isAuthorized({Context context});
  String userId({Context context});
}

class Context {
  State _state = new UnauthorizedState();

  bool get isAuthorized => _state.isAuthorized();

thonglinhma

abstract class Currency {
  String sysmbol();
  String code();
}

class Euro extends Currency {
    @override
    String sysmbol() {
      return "€";
    }

thonglinhma

abstract class Switch {
  Appliance appliance;
  void turnOn();
}

abstract class Appliance {
  void run();
}

class RemoteControl extends Switch {