《Head First 设计模式》学习笔记——命令模式

命令模式也支持可撤销的操作。

// Invoker：要求命令对象运行请求，一般会持有命令对象，能够持有非常多的命令对象。这个是client真正触发命令并要求命令运行对应操作的地方，也就是说相当于使用命令对象的入口。
public class RemoteControl {
	//这时候。遥控器要处理7个开与关的命令，使用对应数组记录这些命令
	Command[] onCommands;
	Command[] offCommands;
 
	public RemoteControl() {
		//在构造器中。仅仅须要实例化并初始化两个开与关的数组
		onCommands = new Command[7];
		offCommands = new Command[7];
		//NoCommand对象是一个空对象（null obeject)的样例。当你不想返回一个有意义的对象时，空对象就非常实用，客户也能够将处理null的责任转义给空对象。

		//举例来说。遥控器不可能一出厂就设置了有意义的命令对象，所以提供了NoCommand对象作为替代品。当调用它的execute()
		//方法时。这样的对象什么也不做。
		Command noCommand = new NoCommand();
		for (int i = 0; i < 7; i++) {
			onCommands[i] = noCommand;
			offCommands[i] = noCommand;
		}
	}
  
	//setCommand()方法须有三个參数，各自是插槽的位置、开的命令、关的命令。
	public void setCommand(int slot, Command onCommand, Command offCommand) {
		onCommands[slot] = onCommand;
		offCommands[slot] = offCommand;
	}
 
	//当按下开或关的button。硬件就会负责调用对应的方法
	public void onButtonWasPushed(int slot) {
		onCommands[slot].execute();
	}
 
	public void offButtonWasPushed(int slot) {
		offCommands[slot].execute();
	}
  
	//覆盖toString()，打印出每一个插槽和它对应的命令。
	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();
	}
}

//定义命令的接口。声明运行的方法。
public interface Command {
	public void execute();
}

//命令接口实现对象，是“虚”的实现。一般会持有接收者，并调用接收者的功能来完毕命令要运行的操作。
public class StereoOnWithCDCommand implements Command {
	Stereo stereo;
 
	public StereoOnWithCDCommand(Stereo stereo) {
		this.stereo = stereo;
	}
 
	public void execute() {
		stereo.on();
		stereo.setCD();
		stereo.setVolume(11);
	}
}

//接收者，真正运行命令的对象。
不论什么类都可能成为一个接收者。仅仅要它能够实现命令要求实现的对应功能。
public class Stereo {
	String location;

	public Stereo(String location) {
		this.location = location;
	}

	public void on() {
		System.out.println(location + " stereo is on");
	}

	public void off() {
		System.out.println(location + " stereo is off");
	}

	public void setCD() {
		System.out.println(location + " stereo is set for CD input");
	}

	public void setDVD() {
		System.out.println(location + " stereo is set for DVD input");
	}

	public void setRadio() {
		System.out.println(location + " stereo is set for Radio");
	}

	public void setVolume(int volume) {
		// code to set the volume
		// valid range: 1-11 (after all 11 is better than 10, right?)
		System.out.println(location + " Stereo volume set to " + volume);
	}
}


//測试
public class RemoteLoader {
 
	public static void main(String[] args) {
		RemoteControl remoteControl = new RemoteControl();
 
		//将所有的装置创建在合适的位置
		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);
 
		//如今已经有了所有的命令。能够将他们载入到遥控器插槽中。
		remoteControl.setCommand(0, livingRoomLightOn, livingRoomLightOff);
		remoteControl.setCommand(1, kitchenLightOn, kitchenLightOff);
		remoteControl.setCommand(2, ceilingFanOn, ceilingFanOff);
		remoteControl.setCommand(3, stereoOnWithCD, stereoOff);
  
		//在这里，使用toString()方法打印出每一个遥控器的插槽和它被指定的命令
		System.out.println(remoteControl);
 
		//一切就绪，逐步按下每一个插槽的开与关button。

		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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