1. interface Playable {
   
2.     void play();
   
3. }
   
4. interface Bounceable {
   
5.    void play();
   
6. }
   
7. interface Rollable extends Playable, Bounceable {
   
8.     Ball ball = new Ball("PingPang");
   
9. }
   
10. class Ball implements Rollable {
    
11.     private String name;
    
12. public String getName() {
    
13.         return name;
    
14.     }
    
15.     public Ball(String name) {
    
16.         this.name = name;            }
    
17.    public void play() {
    
18.           ball = new Ball("Football");
    
19.         System.out.println(ball.getName());
    
20.     }
    
21. }

复制代码

interface Rollable extends Playable, Bounceable {
    Ball ball = new Ball("PingPang");    //error：接口定义的属性必须为public static final，即公有静态常量，且不可为空final，修饰词上就不对，更不要说你这里的Ball对象的创建还依赖于Rollable接口而存在。
}