设计模式--命令模式

一.定义

           命令模式：将一个请求封装为一个命令对象，从而使你可用不同的请求对客户端进行参数化，对请求排队，组合，存储等，以及支持可撤销的操作；

一.类结构图

一.举例

场景：模拟开灯，关灯，开，关音响，调音量命令

命令接受者：Lignt.java;Stereo.java

public class Light {

	String loc = "";

	public Light(String loc) {
		this.loc = loc;
	}

	public void On() {

		System.out.println(loc + " On");
	}

	public void Off() {

		System.out.println(loc + " Off");
	}

}

public class Stereo {
	static int volume = 0;

	public void On() {
		System.out.println("Stereo On");
	}

	public void Off() {
		System.out.println("Stereo Off");
	}

	public void SetCd() {
		System.out.println("Stereo SetCd");
	}

	public void SetVol(int vol) {
		volume = vol;
		System.out.println("Stereo volume=" + volume);
	}

	public int GetVol() {
		return volume;
	}

	public void Start() {
		System.out.println("Stereo Start");
	}
}

命令接口：

public interface Command {
	public void execute();
	public void undo();
}

如下封装命令对象：

public class LightOffCommand implements Command {
	private Light light;
	public LightOffCommand(Light light)
	{
		this.light=light;
	}
	@Override
	public void execute() {
		// TODO Auto-generated method stub
		light.Off();
	}

	@Override
	public void undo() {
		// TODO Auto-generated method stub
		light.On();
	}

}

public class LightOnCommand implements Command {
	private Light light;
	
	public LightOnCommand(Light light)
	{
		this.light=light;
		
	}
	@Override
	public void execute() {
		// TODO Auto-generated method stub
		light.On();
	}

	@Override
	public void undo() {
		// TODO Auto-generated method stub
		light.Off();
	}

}

public class StereoAddVolCommand implements Command {
	private Stereo setreo;
	public StereoAddVolCommand(Stereo setreo)
	{
		this.setreo=setreo;
	}
	
	@Override
	public void execute() {
		// TODO Auto-generated method stub
	int vol=	setreo.GetVol();
	if(vol<11)
	{
		setreo.SetVol(++vol);
	}
		
	}

	@Override
	public void undo() {
		// TODO Auto-generated method stub
	int vol=	setreo.GetVol();
	if(vol>0)
	{
		setreo.SetVol(--vol);
	}
		
	}

.....剩余命令对象略

下面是Invoker对象

public class CommandModeControl implements Control{
	private Command[] onCommands;
	private Command[] offCommands;
	private Stack<Command> stack=new Stack<Command>();
	public CommandModeControl()
	{
		onCommands=new Command[5];
		 offCommands=new Command[5];
		
		 Command noCommand=new NoCommand();
		 
		 for(int i=0,len=onCommands.length;i<len;i++)
		 {
			 onCommands[i]=noCommand;
			 offCommands[i]=noCommand;
		 }
		 
	}
	
	public void setCommand(int slot,Command onCommand,Command offCommand)
	{
		onCommands[slot]=onCommand;
		 offCommands[slot]=offCommand;
		
	}

	@Override
	public void onButton(int slot) {
		
		onCommands[slot].execute();
		stack.push(onCommands[slot]);
	}

	@Override
	public void offButton(int slot) {
		
		offCommands[slot].execute();
		stack.push(offCommands[slot]);
	}

	@Override
	public void undoButton() {
		// TODO Auto-generated method stub
		stack.pop().undo();
	}

Client  客户端

public static void main(String[] args) {
		CommandModeControl control = new CommandModeControl();
		MarcoCommand onmarco,offmarco;
		Light bedroomlight = new Light("BedRoom");
		Light kitchlight = new Light("Kitch");
		Stereo stereo = new Stereo();
		
		
		
		LightOnCommand bedroomlighton = new LightOnCommand(bedroomlight);
		LightOffCommand bedroomlightoff = new LightOffCommand(bedroomlight);
		LightOnCommand kitchlighton = new LightOnCommand(kitchlight);
		LightOffCommand kitchlightoff = new LightOffCommand(kitchlight);

		 Command[] oncommands={bedroomlighton,kitchlighton};
		 Command[] offcommands={bedroomlightoff,kitchlightoff};
			
		onmarco=new MarcoCommand(oncommands);
		offmarco=new MarcoCommand(offcommands);
		
		StereoOnCommand stereoOn = new StereoOnCommand(stereo);
		StereoOffCommand stereoOff = new StereoOffCommand(stereo);
		StereoAddVolCommand stereoaddvol = new StereoAddVolCommand(stereo);
		StereoSubVolCommand stereosubvol = new StereoSubVolCommand(stereo);

		control.setCommand(0, bedroomlighton, bedroomlightoff);
		control.setCommand(1, kitchlighton, kitchlightoff);
		control.setCommand(2, stereoOn, stereoOff);
		control.setCommand(3, stereoaddvol, stereosubvol);
		control.setCommand(4, onmarco, offmarco);

		control.onButton(0);
		control.undoButton();
		//control.offButton(0);
		control.onButton(1);
		control.offButton(1);
		control.onButton(2);
		control.onButton(3);
				
		control.offButton(3);
		control.undoButton();
		control.offButton(2);
		control.undoButton();
		control.onButton(4);
		control.offButton(4);
	}

命令模式的优势：

        命令对象的本质你将命令封装成对象，将发出命令和执行命令的责任分开；这带来的好处有：我们可以对命令进行组合，设计成一个队列；对命令进行存储，放入一个栈结构中，这样就支持回退操作，还可以将命令记录日志；可以很容易的加入新的命令而不影响其他的类。