接口的基本语法

1 interface USB{        //interface定义
2     void write();   //默认public 
3     void read();   //无函数主体, 抽象方法
4 }

1 class USBPhone implements USB{   
2 //implements相当于特殊的extends, 中文叫 实现
3     public void read(){
4         System.out.println("USBPhone read");
5     }
6     public void write(){
7         System.out.println("USBPhone write");
8     }
9 }

1 class Test{
2     public static void main(String args []){
3         USBPhone usbPhone = new USBPhone();
4         USB usb = usbPhone ;    //向上转型后可使用
5         usb.read();
6         usb.write();
7     }
8 }

class Phone implements USB,WiFi{   //一个类实现多个接口
    public void read(){
        System.out.println("USB read");
    }
    public void write(){
        System.out.println("USB write");
    }
    public void open(){
        System.out.println("WiFi read");
    }
    public void close(){
        System.out.println("WiFi read");
    }
}

 1 class Test{
 2     public static void main(String args []){
 3         Phone phone = new Phone();
 4         
 5         USB usb = phone ; 
 6         usb.read();
 7         usb.write();
 8         
 9         WiFi wifi = phone ;
10         wifi.open();
11         wifi.close();
12     }
13 }