命令模式

命令模式:将"请求"封闭成对象,以便使用不同的请求,队列或者日志来参数化其他对象.
命令模式也支持可撤销的损伤.
1.命令模式将发出请求的对象和执行请求的对象解耦.
2.在被解耦的两者之间是通过命令对象进行沟通的.命令对象封装了接收者和一个或一组动作.
3.调用者通过调用命令对象的execute()发出请求,这会使得接收者的动作被调用.
4.调用者可以接受命令当做参数,甚至在运行时动态地进行.
5.命令可以支持撤销,做法是实现一个undo()方法来回到execute()被执行前的状态.
6.宏命令是命令的一种简单的延伸,允许调用多个命令.宏方法也可以支持撤销.
7.实际操作时,很常见使用"聪明"命令对象,也就是直接实现了请求,而不是将工作委托给接收者.
8.命令也可以用来实现日志和事务系统.

package headfirst.command.remote;

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 headfirst.command.remote; 

public class LightOffCommand implements Command { 
Light light; 

public LightOffCommand(Light light) { 
this.light = light; 
} 

public void execute() { 
light.off(); 
} 
} 

 
package headfirst.command.remote; 

public class StereoOnWithCDCommand implements Command { 
Stereo stereo; 

public StereoOnWithCDCommand(Stereo stereo) { 
this.stereo = stereo; 
} 

public void execute() { 
stereo.on(); 
stereo.setCD(); 
stereo.setVolume(11); 
} 
} 



package headfirst.command.remote; 

public class RemoteLoader { 

public static void main(String[] args) { 
RemoteControl 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); 
  
CeilingFanOnCommand ceilingFanOn = 
new CeilingFanOnCommand(ceilingFan); 
CeilingFanOffCommand ceilingFanOff = 
new CeilingFanOffCommand(ceilingFan); 

GarageDoorUpCommand garageDoorUp = 
new GarageDoorUpCommand(garageDoor); 
GarageDoorDownCommand garageDoorDown = 
new GarageDoorDownCommand(garageDoor); 

StereoOnWithCDCommand stereoOnWithCD = 
new StereoOnWithCDCommand(stereo); 
StereoOffCommand  stereoOff = 
new StereoOffCommand(stereo); 

remoteControl.setCommand(0, livingRoomLightOn, livingRoomLightOff); 
remoteControl.setCommand(1, kitchenLightOn, kitchenLightOff); 
remoteControl.setCommand(2, ceilingFanOn, ceilingFanOff); 
remoteControl.setCommand(3, stereoOnWithCD, stereoOff); 
  
System.out.println(remoteControl); 

remoteControl.onButtonWasPushed(0); 
remoteControl.offButtonWasPushed(0); 
remoteControl.onButtonWasPushed(1); 
remoteControl.offButtonWasPushed(1); 
remoteControl.onButtonWasPushed(2); 
remoteControl.offButtonWasPushed(2); 
remoteControl.onButtonWasPushed(3); 
remoteControl.offButtonWasPushed(3); 
} 
}



  


  

    
    
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2008-10-12 21:03
      
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