设计模式之命令模式

命令模式定义:是一个高内聚的模式,将一个请求封装成一个对象,从而让你使用不同的请求把客户端参数化,对请求排队或者记录请求日志,可以提供命令的撤销和恢复操作工作。

优点:

1、类间解耦。

调用者角色与接受者角色(light)之间没有依赖,调用者只需要调用Command的exec方法,不需要知道是那一个接受者执行的。

2、可扩展性。

3、可以和其他模式结合使用。

结合责任链,实现命令族解析任务。

结合模版方法模式,可以减少Command子类的膨胀问题。

缺点:

那就是类膨胀问题。

类图如下:

设计模式之命令模式_第1张图片

代码实现如下:

light类:

package com.designpatterns.command;

public class Light {
	public void on() {
		System.out.println("Light is on");
	}

	public void off() {
		System.out.println("Light is off");
	}
}

Command抽象类:

package com.designpatterns.command;

public interface Command {
	public Light light = new Light();
	public void execute(); 
	public void undo(); 
}

LightOnCommand类:

package com.designpatterns.command;

public class LightOnCommand implements Command {
	@Override
	public void execute() {
		light.on();
	}

	@Override
	public void undo() {
		light.off();
	}

}

LightOffCommand类:

package com.designpatterns.command;

public class LightOffCommand implements Command {
	@Override
	public void execute() {
		light.off();
	}

	@Override
	public void undo() {
		light.on();
	}

}

NoCommand类:

package com.designpatterns.command;

public class NoCommand implements Command {

	@Override
	public void execute() {
	}

	@Override
	public void undo() {
	}

}

控制类:

package com.designpatterns.command;

public class SimepleRemoteControl {
	private Command[] onComands;
	private Command[] offComands;
	private Command undoCommand;

	public SimepleRemoteControl() {
		onComands = new Command[7];
		offComands = new Command[7];
		
		Command noCommand = new NoCommand();
		
		for (int i = 0; i < 7; i++) {
			onComands[i] = noCommand;
			offComands[i] = noCommand;
		}
		undoCommand = noCommand;
	}

	public void setCommand(int slot, Command onCommand,  Command offCommand) {
		onComands[slot] = onCommand;
		offComands[slot] = offCommand;
	}
	
	public void onButtonWasPressed(int slot) {
		onComands[slot].execute();
		undoCommand=onComands[slot];
	}
	
	public void offButtonWasPressed(int slot) {
		offComands[slot].execute();
		undoCommand=offComands[slot];
	}
	
	public void undoButtonWasPushed(){
		undoCommand.undo();
	}
}

测试类:

package com.designpatterns.command;

public class Main {
	public static void main(String[] args) {
		SimepleRemoteControl simepleRemoteControl = new SimepleRemoteControl();
		LightOnCommand lightOnCommand = new LightOnCommand();
		LightOffCommand lightOffCommand = new LightOffCommand();

		simepleRemoteControl.setCommand(0, lightOnCommand, lightOffCommand);
		System.out.println("开灯!");
		simepleRemoteControl.onButtonWasPressed(0);
		System.out.println("关灯!");
		simepleRemoteControl.offButtonWasPressed(0);
		System.out.println("撤销上一步操作!");
		simepleRemoteControl.undoButtonWasPushed();
	}
}

在上面的代码中通过添加undo方法,实现了撤销上一步操作。

这就是命令模式。

参考资料
1、设计模式之禅
2、Head First 设计模式

备注
转载请注明出处
http://blog.csdn.net/wsyw126/article/details/51317887
by WSYW126

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