java USB标准

interface USB{
    public void start();
    public void stop();
}
class Computer{
    public static void plugin(USB usb){
        usb.start();
        System.out.println("=========USB device is working======");
        usb.stop();
    }
};
class Flash implements USB{
    public void start(){
        System.out.println("U-disk starts working...");
    }
    public void stop(){
        System.out.println("U-disk stops working...");
    }
};
class Print implements USB{
    public void start(){
        System.out.println("Printer starts working...");
    }
    public void stop(){
        System.out.println("Printer stops working...");
    }
}

public class InterfaceCaseDemo02 {
    public static void main(String args[]){
        Computer.plugin(new Flash());
        Computer.plugin(new Print());
    }
}

可以看出，计算机关心的只是接口，对于具体设备，毫不关心。