135 lines
2.9 KiB
Java
135 lines
2.9 KiB
Java
## 2. 命令（Command）
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### Intent
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将命令封装成对象中，具有以下作用：
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- 使用命令来参数化其它对象
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- 将命令放入队列中进行排队
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- 将命令的操作记录到日志中
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- 支持可撤销的操作
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### Class Diagram
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- Command：命令
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- Receiver：命令接收者，也就是命令真正的执行者
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- Invoker：通过它来调用命令
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- Client：可以设置命令与命令的接收者
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<div align="center"> <img src="pics/c44a0342-f405-4f17-b750-e27cf4aadde2.png"/> </div><br>
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### Implementation
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设计一个遥控器，可以控制电灯开关。
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<div align="center"> <img src="pics/e6bded8e-41a0-489a-88a6-638e88ab7666.jpg"/> </div><br>
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```java
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public interface Command {
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void execute();
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}
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```
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```java
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public class LightOnCommand implements Command {
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Light light;
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public LightOnCommand(Light light) {
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this.light = light;
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}
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@Override
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public void execute() {
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light.on();
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}
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}
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```
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```java
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public class LightOffCommand implements Command {
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Light light;
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public LightOffCommand(Light light) {
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this.light = light;
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}
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@Override
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public void execute() {
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light.off();
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}
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}
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```
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```java
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public class Light {
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public void on() {
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System.out.println("Light is on!");
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}
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public void off() {
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System.out.println("Light is off!");
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}
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}
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```
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```java
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/**
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* 遥控器
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*/
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public class Invoker {
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private Command[] onCommands;
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private Command[] offCommands;
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private final int slotNum = 7;
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public Invoker() {
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this.onCommands = new Command[slotNum];
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this.offCommands = new Command[slotNum];
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}
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public void setOnCommand(Command command, int slot) {
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onCommands[slot] = command;
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}
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public void setOffCommand(Command command, int slot) {
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offCommands[slot] = command;
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}
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public void onButtonWasPushed(int slot) {
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onCommands[slot].execute();
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}
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public void offButtonWasPushed(int slot) {
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offCommands[slot].execute();
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}
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}
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```
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```java
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public class Client {
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public static void main(String[] args) {
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Invoker invoker = new Invoker();
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Light light = new Light();
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Command lightOnCommand = new LightOnCommand(light);
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Command lightOffCommand = new LightOffCommand(light);
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invoker.setOnCommand(lightOnCommand, 0);
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invoker.setOffCommand(lightOffCommand, 0);
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invoker.onButtonWasPushed(0);
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invoker.offButtonWasPushed(0);
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}
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}
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```
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### JDK
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- [java.lang.Runnable](http://docs.oracle.com/javase/8/docs/api/java/lang/Runnable.html)
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- [Netflix Hystrix](https://github.com/Netflix/Hystrix/wiki)
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- [javax.swing.Action](http://docs.oracle.com/javase/8/docs/api/javax/swing/Action.html)
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<div align="center"><img width="320px" src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/githubio/公众号二维码-2.png"></img></div>
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