JAVA多重继承思考

先贴一段代码(<JAVA编程思想>(中文版)第179页):

interface CanFight {
  void fight();
}

interface CanSwim {
  void swim();
}

interface CanFly {
  void fly();
}

interface CanClimb{
	void climb();
}

class ActionCharacter {
  public void fight() {}
}

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

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

 Hero类组合了基类ActionCharacter和接口CanFlight,CanSwim和CanFly,当通过这种方式将一个具体类和多个接口组合到一起时,具体类必须在前,接口在后(否则会报错).

CanFight接口与ActionCharacter的fight()方法特征签名一样,这样,Hero中就没有必要再提供fight()的定义了,因为这个定义会在编译的初期随着调用ActionCharacter基类而定义好.

这也提示了子类遵循某个接口或继承某个基类的不同之处.用通俗的话可以这样说:

接口是告诉这个类,我有的东西,你必须得有.(即接口有的方法定义,在子类定义时必须都重新定义一遍)

基类是告诉这个子类,我有的东西,你可以拿去用.(即基类有的方法定义,子类可以直接继承下去而不必重新定义)

接口的继承又会是另一种情形,它类似于类的继承.

nterface Sleep
{
	void haveSleep();
}

interface Rest extends Sleep//接口的继承也是用extends关键字
{
	//void haveSleep();//这些都是没 有必要的.
	void haveRest();
}
interface Nap extends Sleep
{
	//void haveSleep();
	void haveNap();
}

interface nod extends Rest, Nap
{
	//void haveSleep();
	//void haveRest();
	//void haveNap();
	void haveNod();
}

class ActionCharacter {  
   public void act() {}  
} 

class ActionCharacter {  
   public void fight() {}  
}