设计模式笔记（20）--命令模式

GOF对命令模式的定义是：“将一个请求封装为一个对象，从而使用户可用不同的请求对客户进行参数化：对请求排队或记录请求日志，并支持可撤销的操作。”

下面以赤壁之战为例，上代码

package Command;

public class Soldiers {
    public void Combinate()
    {
        System.out.println("士兵们集合起来了！");
    }
    
    public void Fight()
    {
        System.out.println("士兵们冲锋陷阵");
    }
    //铁索连舟
    public void CableBoat()
    {
        System.out.println("士兵们把军船用铁栓栓在了一起");
    }
}

package Command;

public abstract class Command {
    protected Soldiers soldiers;
    public Command(Soldiers soldiers)
    {
        this.soldiers = soldiers;
    }
    public abstract void ExcuteCommand();
}

package Command;

public class FightCommand extends Command{

    public FightCommand(Soldiers soldiers) {
        super(soldiers);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void ExcuteCommand() {
        // TODO Auto-generated method stub
        soldiers.Fight();
    }
}

package Command;

public class CombinateCommand extends Command{

    public CombinateCommand(Soldiers soldiers) {
        super(soldiers);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void ExcuteCommand() {
        // TODO Auto-generated method stub
        soldiers.Combinate();
    }
}

package Command;

public class CableBoatCommand extends Command{

    public CableBoatCommand(Soldiers soldiers) {
        super(soldiers);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void ExcuteCommand() {
        // TODO Auto-generated method stub
        soldiers.CableBoat();
    }
}

package Command;

import java.util.ArrayList;
import java.util.List;

//传令官类
public class Herald {
    private List commands = new ArrayList();
    public void SetCommand(Command c)
    {
        commands.add(c);
    }
    public void Notify()
    {
        for(int i = 0;i

package Command;

public class client {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Soldiers soldiers = new Soldiers();
        Command combinateCommand = new CombinateCommand(soldiers);
        Command fightCommand = new FightCommand(soldiers);
        Command cableBoatCommand = new CableBoatCommand(soldiers);
        
        Herald herald = new Herald();
        herald.SetCommand(combinateCommand);
        herald.SetCommand(fightCommand);
        herald.SetCommand(fightCommand);
        herald.SetCommand(cableBoatCommand);
        
        herald.Notify();
        System.out.println("战斗失败了，曹操买来了后悔药");
        
        herald.CancelCommand(cableBoatCommand);
        herald.Notify();
    }
}

命令模式可以很容易地设计一个命令的队列。
命令模式适用于以下几种情况：

1. 需要抽象出待执行动作以便参数化某个对象时
2. 当需要在不同的时刻执行排列以及执行请求时
3. 当系统需要支持取消操作时
4. 当系统需要记录，修改日志时