command pattern

今天把电脑从卧室搬到了阳台终于能见到阳光了，心情不错。这篇blog是在ubuntu弄了一个eclipse和jdk实现了command pattern。越来越觉得pattern好像都一样了，莫非这就是张无忌学太极拳的感觉？不过碰到实际问题的时候能想到运用此pattern才是真正学会了。command pattern可以运用到logging requests，queuing requests。这就是programming to interface的好处了，我只需要调用一个execute方法即可。我想到在unix中所有的东西都当作一个文件来对待应该也是这样的思路了。下面是简化版的代码：

public class Light {String location = "";public Light(String location) {this.location = location;}public void on() {System.out.println(location + " light is on");}public void off() {System.out.println(location + " light is off");}} 

public class LivingroomLightOffCommand implements Command {Light light;public LivingroomLightOffCommand(Light light) {this.light = light;}public void execute() {light.off();}}

package command;public class LivingroomLightOnCommand implements Command {Light light;public LivingroomLightOnCommand(Light light) {this.light = light;}public void execute() {light.on();}}

package command;import java.util.*;//// This is the invoker//public class RemoteControl {Command[] onCommands;Command[] offCommands; public RemoteControl() {onCommands = new Command[7];offCommands = new Command[7]; Command noCommand = new NoCommand();for (int i = 0; i < 7; i++) {onCommands[i] = noCommand;offCommands[i] = noCommand;}} public void setCommand(int slot, Command onCommand, Command offCommand) {onCommands[slot] = onCommand;offCommands[slot] = offCommand;} public void onButtonWasPushed(int slot) {onCommands[slot].execute();} public void offButtonWasPushed(int slot) {offCommands[slot].execute();} public String toString() {StringBuffer stringBuff = new StringBuffer();stringBuff.append("/n------ Remote Control -------/n");for (int i = 0; i < onCommands.length; i++) {stringBuff.append("[slot " + i + "] " + onCommands[i].getClass().getName()+ " " + offCommands[i].getClass().getName() + "/n");}return stringBuff.toString();}} 

package command;public class RemoteLoader { public static void main(String[] args) {RemoteControl remoteControl = new RemoteControl(); Light livingRoomLight = new Light("Living Room"); LightOnCommand livingRoomLightOn = new LightOnCommand(livingRoomLight);LightOffCommand livingRoomLightOff = new LightOffCommand(livingRoomLight);LightOnCommand kitchenLightOn = new LightOnCommand(kitchenLight);LightOffCommand kitchenLightOff = new LightOffCommand(kitchenLight); remoteControl.setCommand(0, livingRoomLightOn, livingRoomLightOff); System.out.println(remoteControl); remoteControl.onButtonWasPushed(0);remoteControl.offButtonWasPushed(0);}} 

书中还有很多其他的command对象，我只取了一个light对象，其他的思路都一样。值得一提的还有就是undo命令，command pattern可以很方便的实现。只需要就一个状态位来保存，如果要undo很多次只需要一个栈来实现即可。