Java: 多态

 1 /*
 2 动物：猫，狗
 3 
 4 */
 5 
 6 abstract class Animal
 7 {
 8     public abstract void eat();
 9 }
10 
11 class Cat extends Animal
12 {
13     public void eat()
14     {
15         System.out.println("吃鱼");
16     }
17     public void catchMouse()
18     {
19         System.out.println("抓老鼠");
20     }
21 }
22 
23 class Dog extends Animal
24 {
25     public void eat()
26     {
27         System.out.println("啃骨头");
28     }
29     public void watchDoor()
30     {
31         System.out.println("看家");
32     }
33 }
34 
35 class Pig extends Animal
36 {
37     public void eat()
38     {
39         System.out.println("吃饲料");
40     }
41     public void gongDi()
42     {
43         System.out.println("拱地");
44     }
45 }
46 
47 class DuoTaiDemo 
48 {
49     public static void main(String[] args) 
50     {
51         Cat c = new Cat();
52         //c.eat();
53         function(c);
54         c.catchMouse();
55 
56         Dog d = new Dog();
57         //d.eat();
58         function(d);
59         d.watchDoor();
60 
61         function(new Pig());
62 
63         System.out.println("上面是普通使用，下面是多态");
64         Animal aCat = new Cat();//类型提升，向上转型
65         function(aCat);
66         Cat bCat = (Cat)aCat;//强制将父类的引用，转成子类类型，向下转型
67         bCat.catchMouse();
68 
69         Animal aDog = new Dog();
70         function(aDog);
71         Animal aPig = new Pig();
72         function(aPig);
73     }
74 
75     public static void function(Animal a)
76     {
77         a.eat();
78     }
79 }