行为型模式--命令模式（Command）

命令模式很好理解，举个例子，司令员下令让士兵去干件事情，从整个事情的角度来考虑，司令员的作用是，发出口令，口令经过传递，传到了士兵耳朵里，士兵去执行。这个过程好在，三者相互解耦，任何一方都不用去依赖其他人，只需要做好自己的事儿就行，司令员要的是结果，不会去关注到底士兵是怎么实现的。我们看看关系图：

Invoker是调用者（司令员），Receiver是被调用者（士兵），MyCommand是命令，实现了Command接口，持有接收对象，看实现代码：

[java]  view plain copy

1. public interface Command {  
2.     public void exe();  
3. }  

[java]  view plain copy

1. public class MyCommand implements Command {  
2.   
3.     private Receiver receiver;  
4.       
5.     public MyCommand(Receiver receiver) {  
6.         this.receiver = receiver;  
7.     }  
8.   
9.     @Override  
10.     public void exe() {  
11.         receiver.action();  
12.     }  
13. }  

[java]  view plain copy

1. public class Receiver {  
2.     public void action(){  
3.         System.out.println("command received!");  
4.     }  
5. }  

[java]  view plain copy

1. public class Invoker {  
2.       
3.     private Command command;  
4.       
5.     public Invoker(Command command) {  
6.         this.command = command;  
7.     }  
8.   
9.     public void action(){  
10.         command.exe();  
11.     }  
12. }  

[java]  view plain copy

1. public class Test {  
2.   
3.     public static void main(String[] args) {  
4.         Receiver receiver = new Receiver();  
5.         Command cmd = new MyCommand(receiver);  
6.         Invoker invoker = new Invoker(cmd);  
7.         invoker.action();  
8.     }  
9. }  

输出：command received!

 

=========================================================
下面是command的另外一个例子：

public class test {

	public static void main(String[] args) {

		Player player = new Player();
		TurnOnCommand on = new TurnOnCommand(player);
		TurnOffCommand off = new TurnOffCommand(player);
		NextCommand next = new NextCommand(player);

		PlayerInvoker invoker = new PlayerInvoker(on, off, next);
		invoker.turnOn();
		invoker.turnOff();
		invoker.next();
	}
}

class Player {

	public void turnOn() {

		System.out.println("打开");
	}

	public void turnOff() {
		System.out.println("关闭");

	}

	public void next() {

		System.out.println("下一曲");
	}
}

interface Command {

	public void execute();
}

class TurnOnCommand implements Command {

	private Player player;

	public TurnOnCommand(Player player) {
		this.player = player;
	}

	public void execute() {
		this.player.turnOn();
	}

}

class TurnOffCommand implements Command {

	private Player player;

	public TurnOffCommand(Player player) {
		this.player = player;
	}

	public void execute() {
		this.player.turnOff();
	}

}

// 下一曲命令类
class NextCommand implements Command {

	private Player player;

	public NextCommand(Player player) {
		this.player = player;
	}

	public void execute() {
		this.player.next();
	}

}

class PlayerInvoker {

	private TurnOnCommand on;
	private TurnOffCommand off;
	private NextCommand next;

	public PlayerInvoker(TurnOnCommand on, TurnOffCommand off, NextCommand next) {
		this.on = on;
		this.off = off;
		this.next = next;
	}

	public void turnOn() {
		this.on.execute();
	}

	public void turnOff() {
		this.off.execute();
	}

	public void next() {
		this.next.execute();
	}
}

 ======================================================

2、

3.代码

public interface Command {
    public void execute();
}


public class ConcreteCommand implements Command {

    private Receiver receiver = null;
    private String state;

    public ConcreteCommand(Receiver receiver){
       this.receiver = receiver;
    }  
    public void execute() {
       receiver.action();
    }
}


public class Receiver {
    public void action(){
       //真正执行命令操作的功能代码
    }
}


public class Invoker {
    private Command command = null;

    public void setCommand(Command command) {
       this.command = command;
    }

    public void runCommand() {
       command.execute();
    }
}

public class Client {
    public void assemble(){
       //创建接收者
       Receiver receiver = new Receiver();
       //创建命令对象，设定它的接收者
       Command command = new ConcreteCommand(receiver);
       //创建Invoker，把命令对象设置进去
       Invoker invoker = new Invoker();
       invoker.setCommand(command);
    }
}

下面给个例子，是模拟对电视机的操作有开机、关机、换台命令。代码如下

//命令接收者
public class Tv {
　　public int currentChannel = 0;

　　public void turnOn() {
　　   System.out.println("The televisino is on.");
　　}

　　public void turnOff() {
　　   System.out.println("The television is off.");
　　}

　　public void changeChannel(int channel) {
　　   this.currentChannel = channel;
　　   System.out.println("Now TV channel is " + channel);
　　}
}

//执行命令的接口
public interface Command {
　　void execute();
}

//开机命令
public class CommandOn implements Command {
　　private Tv myTv;

　　public CommandOn(Tv tv) {
　　   myTv = tv;
　　}

　　public void execute() {
　　   myTv.turnOn();
　　}
}

//关机命令
public class CommandOff implements Command {
　　private Tv myTv;

　　public CommandOff(Tv tv) {
　　   myTv = tv;
　　}

　　public void execute() {
　　   myTv.turnOff();
　　}
}

//频道切换命令
public class CommandChange implements Command {
　　private Tv myTv;

　　private int channel;

　　public CommandChange(Tv tv, int channel) {
　　   myTv = tv;
 　　  this.channel = channel;
　　}

　　public void execute() {
　　   myTv.changeChannel(channel);
　　}
}

//可以看作是遥控器吧
public class Control {
　　private Command onCommand, offCommand, changeChannel;

　　public Control(Command on, Command off, Command channel) {
 　　  onCommand = on;
 　　  offCommand = off;
　　   changeChannel = channel;
　　}

　　public void turnOn() {
　　   onCommand.execute();
　　}

　　public void turnOff() {
　　   offCommand.execute();
　　}

　　public void changeChannel() {
 　　  changeChannel.execute();
　　}
}

//测试类
public class Client {
　　public static void main(String[] args) {
  　　 // 命令接收者
 　　  Tv myTv = new Tv();
 　　  // 开机命令
  　　 CommandOn on = new CommandOn(myTv);
  　　 // 关机命令
  　　 CommandOff off = new CommandOff(myTv);
  　　 // 频道切换命令
 　　  CommandChange channel = new CommandChange(myTv, 2);
 　　  // 命令控制对象
　　   Control control = new Control(on, off, channel);

  　　 // 开机
  　　 control.turnOn();
 　　  // 切换频道
 　　  control.changeChannel();
 　　  // 关机
 　　  control.turnOff();
　　}
}


执行结果为：
The televisino is on.
Now TV channel is 2
The television is off.

4.应用场景