Java设计模式 之 命令模式
1 从属模式分类
行为性模式
2 命令模式意图
命令模式可将动作的请求者和动作的执行者对象中解耦。
该模式将一个行为操作发起者的请求封装到对象中，该请求由另外一个对象执行。
将动作封装成命令对象，这样一来就可以随心所欲的储存、传递、调用。
做多件事，有多种做法。
3 命令模式结构
4 命令模式代码实现
这里假设有一个需要编程实现功能的遥控器，一共有10组开关按钮需要编程来实现不同的控制逻辑。比如说第一组开关可控制客厅的电灯的开关，第二组开关按钮可控制车库门的升起和落下，使用命令模式代码如下：
4.1 ICommon.java
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package com.gof.pattern.command;
/** * 命令接口 * @author Administrator */
public interface ICommand {
// 执行 public void execute();
// 撤销 public void undo();
} |
4.2 Light.java
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package com.gof.pattern.command;
/** * 电灯 * @author Administrator */
public class Light {
private Stringname;
public Light(String name){ this.name = name; }
public void on(){ System.out.println(name +" light is on!"); }
public void off(){ System.out.println(name +" light is off!"); }
} |
4.3 LightOnCommand.java
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package com.gof.pattern.command;
public class LightOnCommand implements ICommand {
private Lightlight;
public LightOnCommand(Light light){ this.light = light; }
@Override public void execute() { light.on(); }
@Override public void undo() { light.off(); } } |
4.4 LightOffCommand.java
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package com.gof.pattern.command;
/** * 关灯 * @author Administrator * */
public class LightOffCommand implements ICommand {
private Lightlight;
public LightOffCommand(Light light){ this.light = light; }
@Override public void execute() { light.off(); }
@Override public void undo() { light.on(); } } |
4.5 Stereo.java
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package com.gof.pattern.command;
/** * 音响 * @author Administrator */
public class Stereo {
private Stringname;
public Stereo(String name){ this.name = name; }
public void on(){ System.out.println(name +" is on!"); }
public void off(){ System.out.println(name +" is off!"); }
public void setCd(){ System.out.println(name +" setCd!"); }
public void setDvd(){ System.out.println(name +" setDvd!"); }
public void setRadio(){ System.out.println(name +" setRadio!"); }
public void setVolume(int size){ System.out.println(name +" setVolume is "+ size +"!"); } }
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4.6 StereoOffWithCDCommand.java
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package com.gof.pattern.command;
/** * 关闭音响 * @author Administrator * */
public class StereoOffWithCDCommand implements ICommand {
private Stereostereo;
public StereoOffWithCDCommand(Stereo stereo){ this.stereo = stereo; }
@Override public void execute() { stereo.off(); }
@Override public void undo() { stereo.setCd(); stereo.setVolume(11); stereo.on(); }
} |
4.7 StereoOnWithCDCommand.java
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package com.gof.pattern.command;
/** * 打开音响 * @author Administrator * */
public class StereoOnWithCDCommand implements ICommand {
private Stereostereo;
public StereoOnWithCDCommand(Stereo stereo){ this.stereo = stereo; }
@Override public void execute() { stereo.setCd(); stereo.setVolume(11); stereo.on(); }
@Override public void undo() { stereo.off(); } }
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4.8 GarageDoor.java
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package com.gof.pattern.command;
/** * 车库实体类 * @author Administrator * */
public class GarageDoor {
private Stringname;
public GarageDoor(String name){ this.name = name; }
public void up(){ System.out.println(name +" is up!"); }
public void down(){ System.out.println(name +" is down!"); }
}
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4.9 GarageDoorUpCommand.java
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package com.gof.pattern.command;
/** * 车库门升起 * @author Administrator */
public class GarageDoorUpCommand implements ICommand {
private GarageDoorgarageDoor;
public GarageDoorUpCommand(GarageDoor garageDoor){ this.garageDoor = garageDoor; }
@Override public void execute() { garageDoor.up(); }
@Override public void undo() { garageDoor.down(); }
}
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4.10 GarageDoorDownCommand.java
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package com.gof.pattern.command;
/** * 车库们落下 * @author Administrator */
public class GarageDoorDownCommand implements ICommand {
private GarageDoorgarageDoor;
public GarageDoorDownCommand(GarageDoor garageDoor){ this.garageDoor = garageDoor; }
@Override public void execute() { garageDoor.down(); }
@Override public void undo() { garageDoor.up(); }
}
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4.11 NoCommand.java
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package com.gof.pattern.command;
/** * 空命令 * @author Administrator * */
public class NoCommand implements ICommand {
@Override public void execute() {}
@Override public void undo() {}
} |
4.12 RemoteControl.java
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package com.gof.pattern.command;
/** * 遥控器 * @author Administrator */
public class RemoteControl {
private ICommand[]onCommands;
private ICommand[]offCommands;
private ICommandundoCommand;
// 初始化遥控器按钮功能 public RemoteControl(){ onCommands = new ICommand[7]; offCommands = new ICommand[7]; ICommand noCommand = new NoCommand(); for(int i=0; i<7; i++){ onCommands[i] = noCommand; offCommands[i] = noCommand; } undoCommand = noCommand; }
public void setCommand(int slot, ICommand onCommand, ICommand offCommand){ onCommands[slot] = onCommand; undoCommand.undo(); offCommands[slot] = offCommand; }
// 按某个位置，on按钮 public void onButtonWasPushed(int solt){ onCommands[solt].execute(); undoCommand = onCommands[solt]; }
// 按某个位置，off按钮 public void offButtonWasPushed(int solt){ offCommands[solt].execute(); undoCommand = offCommands[solt]; }
// 按undo按钮 public void undoButtonWasPushed(){
}
@Override public String toString(){ StringBuffer stringBuff = new StringBuffer(); stringBuff.append("\n------ Remote Control ------\n"); for(int i=0; i<onCommands.length; i++){ stringBuff.append("[solt "+ i +"]" +onCommands[i].getClass().getName() + " " +offCommands[i].getClass().getName() +"\n"); } return stringBuff.toString(); }
}
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4.13 RemoteLoader.java 遥控器测试类
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package com.gof.pattern.command;
public class RemoteLoader {
public static void main(String[] args) {
// 创建一个遥控器 RemoteControl remoteControl = new RemoteControl();
// 将所有装置创建在合适位置 Light livingRoomLight = new Light("Living Room"); Light kitchenLight = new Light("Kitchen"); GarageDoor garageDoor = new GarageDoor(""); Stereo stereo = new Stereo("Living Room");
// 创建所有电灯命令对象 ICommand livingRoomLightOn = new LightOnCommand(livingRoomLight); ICommand livingRoomLightOff = new LightOffCommand(livingRoomLight); ICommand kitchenLightOn = new LightOnCommand(kitchenLight); ICommand kigcchenLightOff = newLightOffCommand(kitchenLight); // 创建车库门上下命令对象 ICommand garageDoorUp = new GarageDoorUpCommand(garageDoor); ICommand garageDoorDown = new GarageDoorDownCommand(garageDoor); // 创建音响开关命令对象 ICommand stereoOnWithCDCommand = new StereoOnWithCDCommand(stereo); ICommand stereoOffWithCdCommand = new StereoOffWithCDCommand(stereo);
// 为遥控器某个位置设置命令 remoteControl.setCommand(0, livingRoomLightOn, livingRoomLightOff); remoteControl.setCommand(1, kitchenLightOn, kigcchenLightOff); remoteControl.setCommand(2, garageDoorUp, garageDoorDown); remoteControl.setCommand(3, stereoOnWithCDCommand, stereoOffWithCdCommand);
System.out.println(remoteControl);
// 我们按下遥控器上的1，2，3，4开关按钮测试 remoteControl.onButtonWasPushed(0); remoteControl.offButtonWasPushed(0);
remoteControl.onButtonWasPushed(1); remoteControl.offButtonWasPushed(1);
remoteControl.onButtonWasPushed(2); remoteControl.offButtonWasPushed(2);
remoteControl.onButtonWasPushed(3); remoteControl.offButtonWasPushed(3);
remoteControl.undoButtonWasPushed(); } }
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5 命令模式总结
5.1 优点
降低了决策逻辑的复杂性
提供了可扩展能力
能够方便地提供撤销操作
能够将多个命令放在一个队列中
能够在不同的线程或远程执行命令
5.2 缺点
在对象的创建、销毁及使用过程中可能会增加系统开销
使应用程序的结构更加复杂
5.3 指导原则
封装变化
多用组合，少用继承
针对接口编程，不针对实现编程
为交互对象之间松耦合设计而努力
类应该对扩展开发，对修改关闭
依赖抽象，不依赖具体类
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命令模式：将请求封装成对象，这可以让你使用不同的请求、队列、或者日志请求来参数化其它对象。命令模式也可以支持撤销操作。 |
