笔记本接口实现案例

package duotai.lianxi1.lainxi2;

public class Computer  {
    public void powerOn(){
        System.out.println("开机");
    }
    public void poweroff(){
        System.out.println("关机");
    }
    //使用USB设备的方法 使用接口作为方法的参数
    public void usbDe(Usb usb){
        usb.open();  //打开设备
        if (usb instanceof Mouse){
            Mouse mouse=(Mouse) usb;   // 一点要先判断
            mouse.click();             //向下转型
        }
        else if (usb instanceof Keyboard){     //先判断
            Keyboard keyboard=(Keyboard) usb;   //向下转型
            keyboard.tyep();
        }
        usb.close();  //关闭设备
    }
}
~~~~~~~~  


package duotai.lianxi1.lainxi2;
//
public class Keyboard implements Usb {
    @Override
    public void open() {
        System.out.println("打开键盘");
    }

    @Override
    public void close() {
        System.out.println("关闭键盘");
    }
    public static void tyep(){
        System.out.println("键盘输入");
    }
}


~~删除线格式~~ 

package duotai.lianxi1.lainxi2;

public class Mouse implements Usb {
    @Override
    public void open() {
        System.out.println("打开鼠标");
    }

    @Override
    public void close() {
        System.out.println("关闭鼠标");
    }
    public static void click(){
        System.out.println("点击鼠标");
    }
}

====

package duotai.lianxi1.lainxi2;

public class Test {
    public static void main(String[] args) {
        Computer computer1=new Computer();
        computer1.powerOn();
        Mouse mouse=new Mouse();
        //先向上转型为接口 然后再调用
        Usb usbmouse=mouse;  //多态写法
        //参数是Usb接口类型鼠标
        computer1.usbDe(usbmouse);
        //  创建一个usb键盘
        Keyboard keyboard=new Keyboard();//没有写多态写法
        //方法参数是Usb类型，传递进去的是实现类对象
        computer1.usbDe(keyboard);   //正确写法 也发生了向上转型
        //使用子类对象 匿名对象也是可以的
//        computer1.usbDe(new Keyboard()); 也是正确写法


        computer1.poweroff();
        System.out.println("======例子");

        method(10.0);//正确写法 double-->double
        method(10);//正确写法 int-->double
        int a=10;
        method(a);//正确写法 int-->double
    }
    public static void method(double n){
        System.out.println(n);
    }
}

====
package duotai.lianxi1.lainxi2;

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