安全向下转移--instanceof

格式：对象 instanceof 类名称

package zhuanxing;

public class main {
    public static void main(String[] args) {
        animal1 animal1=new dog();
        animal1.eat();
        if (animal1 instanceof dog1){
            dog1 dog1 =(zhuanxing.dog1)animal1;
            dog1.eat1();
        }
       if (animal1 instanceof dog){
           dog dog=(zhuanxing.dog)animal1;
           dog.eat2();

       }

    }
}

练习：笔记本调用usb接口类

接口

package benjiben;

public interface USB {
    public abstract void open();
    public abstract void off();


    }

鼠标类

package benjiben;

import java.util.Scanner;

public class mouse  implements USB{
    @Override
    public void open() {
        System.out.println("打开鼠标成功");
    }

    @Override
    public void off() {
        System.out.println("关闭鼠标成功");
    }
    public void click(){
        Scanner sc=new Scanner(System.in);
        System.out.println("鼠标正在点击");
        int a=sc.nextInt();
        System.out.println("鼠标点击了"+a+"下！");
    }
}

键盘类

package benjiben;

import java.util.Scanner;

public class keyboard implements USB{
    @Override
    public void open() {
        System.out.println("打开键盘成功");
    }

    @Override
    public void off() {
        System.out.println("关闭键盘成功");
    }
    public void input(){
        Scanner scanner=new Scanner(System.in);
        System.out.println("请在键盘输入");
        String a=scanner.next();
        int zm=0;
        int sz=0;
        int qt=0;
        {char[] chars = a.toCharArray();
        for (int i = 0; i < chars.length; i++) {
            char dg =chars[i];
            if ('A'<=dg && dg<='z'){
                zm++;}
            else if ('0'<=dg && dg<='9'){
                sz++;
            }else {
                qt++;
            }



    }
            System.out.println("键盘输入了:"+a);
            System.out.println("其中字母有："+zm+"个");
            System.out.println("数字有"+sz+"个");
            System.out.println("其他有"+qt+"个");}
}}

笔记本了类

package benjiben;

public class computer {
    public void Poweron(){
        System.out.println("电脑开机！");
    }
    public void Poweroff(){
        System.out.println("电脑关机！");
    }
    public void use(USB usb){
        usb.open();
        if (usb instanceof mouse){
            mouse mouse=(benjiben.mouse)usb;
            mouse.click();
        }else if (usb instanceof keyboard){
            keyboard keyboard=(benjiben.keyboard)usb;
            keyboard.input();
        }
        usb.off();
    }
}

主方法

package benjiben;

public class diannao {
    public static void main(String[] args) {
        computer computer=new computer();//创建电脑
        computer.Poweron();//电脑开机
        USB usb= new mouse();//准备鼠标
        computer.use(usb);//电脑使用鼠标
        keyboard keyboard=new keyboard();//准备键盘
        computer.use(keyboard);//电脑使用键盘
        computer.Poweroff();//电脑关机
    }
}