命令模式

命令模式指将一个请求封装成一个对象，用不同的请求对客户进行参数化。
通过调用者调用接受者，接收者执行命令（调用者→接受者→命令）

以空调遥控器为例子

新建一个空调对象

public class AirConditioner {
	
	String host = "http://www.xxx.com/";

}

新建Command 抽象类

public abstract class Command {
	
	public abstract void run();
	
	public abstract void undo();

}

新建开命令对象

public class ONCommand extends Command {

	private AirConditioner airConditioner;
	
	private String command = "ON"; 
	
	
	public ONCommand(AirConditioner airConditioner) {
		this.airConditioner = airConditioner;
	}

	@Override
	public void run() {
		airConditioner.host = airConditioner.host+command;
		System.out.println(airConditioner.host);
	}

	@Override
	public void undo() {
		airConditioner.host = airConditioner.host.substring(0, airConditioner.host.length()-command.length());
		System.out.println(airConditioner.host);
	}

}

新建关命令

public class OFFCommand extends Command {

private AirConditioner airConditioner;
	
	private String command = "OFF"; 
	
	public OFFCommand(AirConditioner airConditioner) {
		this.airConditioner = airConditioner;
	}

	@Override
	public void run() {
		airConditioner.host = airConditioner.host+command;
		System.out.println(airConditioner.host);
	}

	@Override
	public void undo() {
		airConditioner.host = airConditioner.host.substring(0, airConditioner.host.length()-command.length());
		System.out.println(airConditioner.host);
	}

}

调用相应的接收者执行命令

public class Test {
	
	public static void main(String[] args) {
		AirConditioner airConditioner = new AirConditioner();
		Command onCommand = new ONCommand(airConditioner);
		onCommand.run();
		onCommand.undo();
		
		Command offCommand = new OFFCommand(airConditioner);
		offCommand.run();
		offCommand.undo();
	}

}

结果