Java Abstract class and Interface 实例化解析

//: Adventure.java
// Multiple interfaces
import java.util.*;

interface CanFight {
  void fight();
}

interface CanSwim {
  void swim();
}

interface CanFly {
  void fly();
}

class ActionCharacter {
  public void fight() {}
}

class Hero extends ActionCharacter 
    implements CanFight, CanSwim, CanFly {
  public void swim() {}
  public void fly() {}
}

public class Adventure {
  static void t(CanFight x) { x.fight(); }
  static void u(CanSwim x) { x.swim(); }
  static void v(CanFly x) { x.fly(); }
  static void w(ActionCharacter x) { x.fight(); }
  public static void main(String[] args) {
    Hero i = new Hero();
    t(i); // Treat it as a CanFight
    u(i); // Treat it as a CanSwim
    v(i); // Treat it as a CanFly
    w(i); // Treat it as an ActionCharacter

  }
} ///:~

对于Hero集成了Interface CanFight,但是在Class Hero中却没有定义void fight()函数进行实现，但是Java编译却没有提示出错.

原因：在Hero继承的子类ActionCharacter中有定义void fight()函数，此函数可以被Hero直接继承过来。因此，此Interface CanFight没有提示错误。

Abstract class可以有自己的默认可实现的函数，但是Interface只能是函数类型申明，不可以显示具体内容。