接口应用

interface USB {
    public abstract void open();
    public abstract void close();
}

public class BookPC {

    
    public static void main(String[] args) {
        useUSB(new Mouse());
        
    }

    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
        u.open();
        u.close();
    }
}

class Mouse implements USB {
    public void open() {
        System.out.println("open Mouse..");
    }
    public void close() {
        System.out.println("close Mouse..");
    }
}