Exemplo Dart herança

main.dart

class Television {
  
  void _illuminateDisplay() {
    print ("Display ON");
  }
  
  void _activateIrSensor() {
    print ("IR sensor ON");
  }
  
  void turnOn() {
    _illuminateDisplay();
    _activateIrSensor();
  }
  
}

class SmartTelevision extends Television {
  void _bootNetworkInterface() {
    print ("Network booted");
  }
  
  void _initializeMemory() {
    print ("Reading memory");
    print ("X memory ready");
  }
  
  void _upgradeApps() {
    print ("Checking Apps new versions");
  }
  
  void turnOn() {
    super.turnOn();
    _bootNetworkInterface();
    _initializeMemory();
    _upgradeApps();
  }
  
}

void main () {
  Television t = new Television();
  
  print("Turning on Television");
  t.turnOn();
  
  print("");
  
  print("Turning on SmartTv");
  SmartTelevision s = new SmartTelevision();
  
  s.turnOn();
}