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

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

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

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

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

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 +"!");

}

}

4.6    StereoOffWithCDCommand.java

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

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();

}

}

4.8    GarageDoor.java

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!");

}

}

4.9    GarageDoorUpCommand.java

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();

}

}

4.10       GarageDoorDownCommand.java

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();

}

}

4.11       NoCommand.java

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

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();

}

}

4.13       RemoteLoader.java 遥控器测试类

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);

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();

}

}

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

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。