白话设计模式_命令模式2：撤销、宏命令示例

       上篇介绍了命令模式的理论知识，这里再写两个小例子，加深理解。

     1、撤销命令，关键在于命令执行的时侯保存这个命令对象，这就是把操作封装成对象的好处。

//这个不变
public class Light {
	public void off(){
		System.out.println("off...");
	}	
	public void on(){
		System.out.println("on...");
	}
}

//Command接口添加一个undo()
public interface Command {
	public void execute();	
	public void undo();
}
public class LightOffCommand implements Command {
	Light light;
	public LightOffCommand(Light light){
		this.light = light;
	} 
	
	public void execute() {
		light.off();
	}
	//在这里进行之前操作的逆操作，实现“撤销”
	public void undo(){
		light.on();
	}
}
public class LightOnCommand implements Command {
	Light light;
	public LightOnCommand(Light light){
		this.light = light;
	}
	public void execute() {
		light.on();
	}
	
	public void undo(){
		light.off();
	}
}
public class RemoteControl {
	Command c;
	Command lastCommand;
	public void setCommand(Command c){
		this.c = c;
	}
	public void pressButton(){
		c.execute();
                //保存命令对象的引用
                lastCommand = c;
	}
	public void undoPressButton(){
		lastCommand.undo();
	}
}

      测试:

public class CommandLoader {
	public static void main(String[] args) {
		RemoteControl src = new RemoteControl();
		Light light = new Light();
		LightOnCommand lo = new LightOnCommand(light);
		src.setCommand(lo);
		//操作
		src.pressButton();
		System.out.println();
                //撤销操作
		src.undoPressButton();
	}
}

      输出:

on...
off...

      这里模拟的是简单操作，实际上可能有针对Light状态值的操作，但实现原理是一样的。

     2、宏命令：创建一个新类MacroCommand，封装多个命令，达到一次性执行多个命令的目的。

//此类与一般的具体命令是一个级别的
public class MacroCommand implements Command{
        //保存多个命令对象
	Command[] commands;
	
	public MacroCommand(Command[] commands) {
		this.commands = commands;
	}
	
	public void execute(){
		for (Command c : commands) {
			c.execute();
		}
	}
}

public class CommandLoader {
	public static void main(String[] args) {
                //遥控器
                RemoteControl rc = new RemoteControl();
		//三个命令
                LightOnCommand lo = new LightOnCommand(new Light());
		TvOnCommand to = new TvOnCommand(new Tv());
		AirConditionOnCommand ao = new AirConditionOnCommand(new AirCondition());
		
		Command[] cs = {lo,to,ao};
                //宏命令
                MacroCommand mc = new MacroCommand(cs);
		
		rc.setCommand(mc);
		rc.pressButton();
	}
}

       执行结果是：

on...
tv on...
air condition on...