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notes/设计模式 - 命令.md

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