抽象类继承和接口

abstract class Demo{
    abstract void method1(); 
    abstract void method2(); 
    ...
}
interface Demo {
    void method1();
    void method2();
  ...
}

abstrat class Door{
    abstract void open();
    abstract void close();
}
interface Alarm {
    void alarm();
}
class AlarmDoor extends Door implements Alarm {
    void open() {...}
    void close() {...}
    void alarm() {...}
}