接口应用

 1 interface USB {
 2     public abstract void open();
 3     public abstract void close();
 4 }
 5 
 6 public class BookPC {
 7 
 8     
 9     public static void main(String[] args) {
10         useUSB(new Mouse());
11         
12     }
13 
14     public static void useUSB(USB u) {    //接口类型的引用，用于接收（指向）接口的对象子类
15         u.open();
16         u.close();
17     }
18 }
19 
20 class Mouse implements USB {
21     public void open() {
22         System.out.println("open Mouse..");
23     }
24     public void close() {
25         System.out.println("close Mouse..");
26     }
27 }