#PrefaceBefore you start sharing, please think about three questions.
1. What is polymorphism?
2. There are several ways to implement polymorphism (in addition to interfaces, what else can achieve polymorphism? The answer is not unique.)
3. The benefits of polymorphism
Answer: Everyone can share their insights to In the comments below
, polymorphism is implemented in the form of interfaces.
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From this relationship diagram, you can see the relationship between the interface and the computer. And the relationship between the interface and the mouse and keyboard.
package cn.itcast.day10.demo07;public interface USB {
void open();//打开设备
void close();//关闭设备}Keyboard class: implement USB interface
package cn.itcast.day10.demo07;//键盘本身就是一个USB设备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");
}}Mouse class: implement USB interface
package cn.itcast.day10.demo07;//鼠标本身就是一个USB设备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");
}} Computer class: Using USB interface
package cn.itcast.day10.demo07;public class Computer {
//电脑本身自带的功能
public void powerOn(){
System.out.println("笔记本电脑开机");
}
public void powerOff(){
System.out.println("笔记本电脑关机");
}
//使用USB接口方法
public void useDevice(USB usb){
usb.open();
usb.close();
}}Client class:
package cn.itcast.day10.demo07;public class DemoMain {
public static void main(String[] args) {
Computer computer=new Computer();//实例化电脑
//省略向上转型
computer.powerOn();
computer.useDevice(new Mouse());
//使用向上转型
USB usb=new keyboard();
computer.useDevice(usb);
computer.powerOff();
}}Result
Programming video
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