命令模式(command pattern) 撤销(undo) 详细解释

本文地址: http://blog.csdn.net/caroline_wendy

參考命令模式: http://blog.csdn.net/caroline_wendy/article/details/31379977

命令模式能够用于运行撤销(undo)操作.

详细方法:

1. 对象类中须要保存状态, 如level.

package command;public class CeilingFan {String location = "";int level;public static final int HIGH = 3;public static final int MEDIUM = 2;public static final int LOW = 1;public static final int OFF = 0;public CeilingFan(String location) {this.location = location;}public void high() {// turns the ceiling fan on to highlevel = HIGH;System.out.println(location + " ceiling fan is on high");} public void medium() {// turns the ceiling fan on to mediumlevel = MEDIUM;System.out.println(location + " ceiling fan is on medium");}public void low() {// turns the ceiling fan on to lowlevel = LOW;System.out.println(location + " ceiling fan is on low");}public void off() {// turns the ceiling fan offlevel = OFF;System.out.println(location + " ceiling fan is off");}public int getSpeed() {return level;}
}

2. 命令接口, 包括撤销(undo)操作, 即依据传入对象的状态參数, 推断详细的撤销动作.

/*** @time 2014年6月9日*/
package command;/*** @author C.L.Wang**/
public interface Command {public void execute();public void undo(); //撤销
}

3. 详细命令(Concrete Command)类须要实现, 撤销操作, 依据不同状态, 运行不同的撤销操作.

/*** @time 2014年6月16日*/
package command;/*** @author C.L.Wang**/
public class CeilingFanHighCommand implements Command {CeilingFan ceilingFan;int prevSpeed;public CeilingFanHighCommand(CeilingFan ceilingFan) {this.ceilingFan = ceilingFan;}/* (non-Javadoc)* @see command.Command#execute()*/@Overridepublic void execute() {// TODO Auto-generated method stubprevSpeed = ceilingFan.getSpeed();ceilingFan.high();}/* (non-Javadoc)* @see command.Command#undo()*/@Overridepublic void undo() {// TODO Auto-generated method stubif (prevSpeed == CeilingFan.HIGH) {ceilingFan.high();} else if (prevSpeed == CeilingFan.MEDIUM) {ceilingFan.medium();} else if (prevSpeed == CeilingFan.LOW) {ceilingFan.low();} else if (prevSpeed == CeilingFan.OFF) {ceilingFan.off();}}}package command;public class CeilingFanMediumCommand implements Command {CeilingFan ceilingFan;int prevSpeed;public CeilingFanMediumCommand(CeilingFan ceilingFan) {this.ceilingFan = ceilingFan;}public void execute() {prevSpeed = ceilingFan.getSpeed();ceilingFan.medium();}public void undo() {if (prevSpeed == CeilingFan.HIGH) {ceilingFan.high();} else if (prevSpeed == CeilingFan.MEDIUM) {ceilingFan.medium();} else if (prevSpeed == CeilingFan.LOW) {ceilingFan.low();} else if (prevSpeed == CeilingFan.OFF) {ceilingFan.off();}}
}package command;public class CeilingFanLowCommand implements Command {CeilingFan ceilingFan;int prevSpeed;public CeilingFanLowCommand(CeilingFan ceilingFan) {this.ceilingFan = ceilingFan;}public void execute() {prevSpeed = ceilingFan.getSpeed();ceilingFan.low();}public void undo() {if (prevSpeed == CeilingFan.HIGH) {ceilingFan.high();} else if (prevSpeed == CeilingFan.MEDIUM) {ceilingFan.medium();} else if (prevSpeed == CeilingFan.LOW) {ceilingFan.low();} else if (prevSpeed == CeilingFan.OFF) {ceilingFan.off();}}
}package command;public class CeilingFanOffCommand implements Command {CeilingFan ceilingFan;int prevSpeed;public CeilingFanOffCommand(CeilingFan ceilingFan) {this.ceilingFan = ceilingFan;}public void execute() {prevSpeed = ceilingFan.getSpeed();ceilingFan.off();}public void undo() {if (prevSpeed == CeilingFan.HIGH) {ceilingFan.high();} else if (prevSpeed == CeilingFan.MEDIUM) {ceilingFan.medium();} else if (prevSpeed == CeilingFan.LOW) {ceilingFan.low();} else if (prevSpeed == CeilingFan.OFF) {ceilingFan.off();}}
}

4. 接受者(Receiver)类实现撤销(undo)操作, 即在调用命令时, 保留命令, 运行撤销(undo)操作时, 调用保留的命令.

/*** @time 2014年6月16日*/
package command;/*** @author C.L.Wang**/
public class RemoteControl {Command[] onCommands; //开Command[] offCommands; //关Command undoCommand; //撤销public RemoteControl() {onCommands = new Command[7];offCommands = new Command[7];Command noCommand = new NoCommand();for (int i=0; i<7; ++i) { //初始化onCommands[i] = noCommand;offCommands[i] = noCommand;}undoCommand = noCommand;}public void setCommand (int slot, Command onCommand, Command offCommand) {this.onCommands[slot] = onCommand;this.offCommands[slot] = offCommand;}public void onButtonWasPushed(int slot) { //开启buttononCommands[slot].execute();undoCommand = onCommands[slot];}public void offButtonWasPushed(int slot) { //关闭buttonoffCommands[slot].execute();undoCommand = offCommands[slot];}public void undoButtonWasPushed() {undoCommand.undo();}public String toString() {StringBuffer stringBuffer = new StringBuffer();stringBuffer.append("\n------ Remote Control ------\n");for (int i=0; i<onCommands.length; ++i) {stringBuffer.append("[slot " + i + "] " + onCommands[i].getClass().getName()+ "    " + offCommands[i].getClass().getName() + "\n");}return stringBuffer.toString();}
}

5. 測试类, 调用不同的命令, 保存不同的状态, 运行撤销操作.

/*** @time 2014年6月16日*/
package command;import javax.crypto.spec.IvParameterSpec;/*** @author C.L.Wang**/
public class RemoteLoader {/*** @param args*/public static void main(String[] args) {// TODO Auto-generated method stubRemoteControl remoteControl = new RemoteControl();Light livingRoomLight = new Light("Living Room");Light kitchenLight = new Light("Kitchen");CeilingFan ceilingFan = new CeilingFan("Living Room");GarageDoor garageDoor = new GarageDoor("");Stereo stereo = new Stereo("Living Room");LightOnCommand livingRoomLightOn = new LightOnCommand(livingRoomLight);LightOffCommand livingRoomLightOff = new LightOffCommand(livingRoomLight);LightOnCommand kitchenLightOn = new LightOnCommand(kitchenLight);LightOffCommand kitchenLightOff = new LightOffCommand(kitchenLight);CeilingFanHighCommand ceilingFanHigh = new CeilingFanHighCommand(ceilingFan);CeilingFanMediumCommand ceilingFanMedium = new CeilingFanMediumCommand(ceilingFan);CeilingFanOffCommand ceilingFanOff = new CeilingFanOffCommand(ceilingFan);GarageDoorOnCommand garageDoorOn = new GarageDoorOnCommand(garageDoor);GarageDoorOffCommand garageDoorOff = new GarageDoorOffCommand(garageDoor);StereoOnWithCDCommand stereoOnWithCD = new StereoOnWithCDCommand(stereo);StereoOffCommand stereoOffCommand = new StereoOffCommand(stereo);remoteControl.setCommand(0, livingRoomLightOn, livingRoomLightOff); //设这遥控器remoteControl.setCommand(1, kitchenLightOn, kitchenLightOff);remoteControl.setCommand(2, ceilingFanHigh, ceilingFanOff);remoteControl.setCommand(3, ceilingFanMedium, ceilingFanOff);remoteControl.setCommand(4, stereoOnWithCD, stereoOffCommand);remoteControl.onButtonWasPushed(2); //快速remoteControl.offButtonWasPushed(2); //关闭快速System.out.println(remoteControl);remoteControl.undoButtonWasPushed(); //退回快速System.out.println();remoteControl.onButtonWasPushed(3); //中速System.out.println(remoteControl);remoteControl.undoButtonWasPushed(); //快速}}

6. 输出:

Living Room ceiling fan is on high
Living Room ceiling fan is off------ Remote Control ------
[slot 0] command.LightOnCommand    command.LightOffCommand
[slot 1] command.LightOnCommand    command.LightOffCommand
[slot 2] command.CeilingFanHighCommand    command.CeilingFanOffCommand
[slot 3] command.CeilingFanMediumCommand    command.CeilingFanOffCommand
[slot 4] command.StereoOnWithCDCommand    command.StereoOffCommand
[slot 5] command.NoCommand    command.NoCommand
[slot 6] command.NoCommand    command.NoCommandLiving Room ceiling fan is on highLiving Room ceiling fan is on medium------ Remote Control ------
[slot 0] command.LightOnCommand    command.LightOffCommand
[slot 1] command.LightOnCommand    command.LightOffCommand
[slot 2] command.CeilingFanHighCommand    command.CeilingFanOffCommand
[slot 3] command.CeilingFanMediumCommand    command.CeilingFanOffCommand
[slot 4] command.StereoOnWithCDCommand    command.StereoOffCommand
[slot 5] command.NoCommand    command.NoCommand
[slot 6] command.NoCommand    command.NoCommandLiving Room ceiling fan is on high

其余代码下载: http://download.csdn.net/detail/u012515223/7507147