摘要：要點(diǎn)命令模式將發(fā)出請(qǐng)求的對(duì)象和執(zhí)行請(qǐng)求的對(duì)象解耦。感謝你看到這里，命令模式到這里就結(jié)束了，本人文筆隨便，若有不足或錯(cuò)誤之處望給予指點(diǎn)，度彎腰很快我會(huì)發(fā)布下一個(gè)設(shè)計(jì)模式的內(nèi)容，生命不息，編程不止

繼續(xù)上部分的說

在之前的文章最后寫了一個(gè)帶有撤銷電燈功能的遙控器功能，通常，想要實(shí)現(xiàn)撤銷的功能，需要記錄撤銷之前的狀態(tài)是什么，就比方說電扇，允許有多個(gè)風(fēng)速狀態(tài)，也允許被關(guān)閉。
直接上代碼。

1、風(fēng)扇類

package CeilingFan;
/**
 * 使用狀態(tài)實(shí)現(xiàn)撤銷
 * 風(fēng)扇類
 * @author Joy
 * 
 */
public class CeilingFan {
    public static final int HIGH = 3;
    public static final int MEDIUM = 2;
    public static final int LOW = 1;
    public static final int OFF = 0;
    String location;
    int speed;

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

    // 高轉(zhuǎn)速
    public void high() {
        speed = HIGH;
        System.out.println(location+"風(fēng)扇正在高轉(zhuǎn)速運(yùn)行");
    }

    // 中轉(zhuǎn)速
    public void medium() {
        speed = MEDIUM;
        System.out.println(location+"風(fēng)扇正在中轉(zhuǎn)速運(yùn)行");
    }

    // 低轉(zhuǎn)速
    public void low() {
        speed = LOW;
        System.out.println(location+"風(fēng)扇正在低轉(zhuǎn)速運(yùn)行");
    }

    // 關(guān)閉吊扇
    public void off() {
        speed = OFF;
        System.out.println(location+"風(fēng)扇關(guān)閉");
    }
    
    //獲取當(dāng)前吊扇速度
    public int getSpeed(){
        return speed;
    }
}

2、命令類

package CeilingFan;

public interface Command {
    public void execute();

    public void undo();
}

3、下面是風(fēng)扇高、中、低關(guān)閉的具體實(shí)現(xiàn)類

package CeilingFan;

/**
 * 風(fēng)扇高速操作
 * 
 * @author Joy
 * 
 */
public class CeilingFanHighCommand implements Command {
    CeilingFan ceilingFan;
    int prevSpeed;

    public CeilingFanHighCommand(CeilingFan ceilingFan) {
        this.ceilingFan = ceilingFan;
    }

    // 執(zhí)行
    @Override
    public void execute() {
        // 執(zhí)行方法前，先獲取之前的狀態(tài)并記錄下來
        prevSpeed = ceilingFan.getSpeed();
        ceilingFan.high();
    }

    // 撤銷
    @Override
    public void undo() {
        // 將風(fēng)扇的速度設(shè)置為之前的狀態(tài)，達(dá)到撤銷目的
        switch (prevSpeed) {
        case CeilingFan.HIGH:
            ceilingFan.high();
            break;
        case CeilingFan.MEDIUM:
            ceilingFan.medium();
            break;
        case CeilingFan.LOW:
            ceilingFan.low();
            break;
        case CeilingFan.OFF:
            ceilingFan.off();
            break;
        }
    }
}

package CeilingFan;
/**
 * 風(fēng)扇中速操作
 * @author Joy
 *
 */
public class CeilingFanMediumCommand implements Command {
    CeilingFan ceilingFan;
    int prevSpeed;

    public CeilingFanMediumCommand(CeilingFan ceilingFan) {
        this.ceilingFan = ceilingFan;
    }

    public void execute() {
        prevSpeed = ceilingFan.getSpeed();
        ceilingFan.medium();
    }

    public void undo() {
        switch (prevSpeed) {
        case CeilingFan.HIGH:
            ceilingFan.high();
            break;
        case CeilingFan.MEDIUM:
            ceilingFan.medium();
            break;
        case CeilingFan.LOW:
            ceilingFan.low();
            break;
        default:
            ceilingFan.off();
            break;
        }
    }
}

package CeilingFan;
/**
 * 風(fēng)扇低速操作
 * @author Joy
 *
 */
public class CeilingFanLowCommand implements Command {
    CeilingFan ceilingFan;
    int prevSpeed;

    public CeilingFanLowCommand(CeilingFan ceilingFan) {
        this.ceilingFan = ceilingFan;
    }

    @Override
    public void execute() {
        prevSpeed = ceilingFan.getSpeed();
        ceilingFan.low();

    }

    @Override
    public void undo() {
        switch (prevSpeed) {
        case CeilingFan.HIGH:
            ceilingFan.high();
            break;
        case CeilingFan.MEDIUM:
            ceilingFan.medium();
            break;
        case CeilingFan.LOW:
            ceilingFan.low();
            break;
        default:
            ceilingFan.off();
            break;
        }
    }
}

package CeilingFan;
/**
 * 風(fēng)扇關(guān)閉
 * @author Joy
 *
 */
public class CeilingFanOffCommand implements Command {
    CeilingFan ceilingFan;
    int prevSpeed;

    public CeilingFanOffCommand(CeilingFan ceilingFan) {
        this.ceilingFan = ceilingFan;
    }

    public void execute() {
        prevSpeed = ceilingFan.getSpeed();
        ceilingFan.off();
    }

    public void undo() {
        switch (prevSpeed) {
        case CeilingFan.HIGH:
            ceilingFan.high();
            break;
        case CeilingFan.MEDIUM:
            ceilingFan.medium();
            break;
        case CeilingFan.LOW:
            ceilingFan.low();
            break;
        default:
            ceilingFan.off();
            break;
        }
    }
}

4、無操作類接口

package CeilingFan;

public class NoCommand implements Command {
    public void execute() { }
    public void undo() { }
}

5、調(diào)用者

package CeilingFan;
/**
 * 調(diào)用者
 * @author Joy
 *
 */
public class RemoteControlWithUndo {
    Command[] onCommands;
    Command[] offCommands;
    Command undoCommand;
 
    public RemoteControlWithUndo() {
        onCommands = new Command[7];
        offCommands = new Command[7];
 
        Command noCommand = new NoCommand();
        for(int i=0;i<7;i++) {
            onCommands[i] = noCommand;
            offCommands[i] = noCommand;
        }
        undoCommand = noCommand;
    }
  
    public void setCommand(int slot, Command onCommand, Command offCommand) {
        onCommands[slot] = onCommand;
        offCommands[slot] = offCommand;
    }
 
    public void onButtonWasPushed(int slot) {
        onCommands[slot].execute();
        undoCommand = onCommands[slot];
    }
 
    public void offButtonWasPushed(int slot) {
        offCommands[slot].execute();
        undoCommand = offCommands[slot];
    }
 
    public void undoButtonWasPushed() {
        undoCommand.undo();
    }
  
    public String toString() {
        StringBuffer stringBuff = new StringBuffer();
        stringBuff.append("
------ 遙控器 -------
");
        for (int i = 0; i < onCommands.length; i++) {
            stringBuff.append("[插槽 " + i + "] " + onCommands[i].getClass().getName()
                + "    " + offCommands[i].getClass().getName() + "
");
        }
        stringBuff.append("[撤銷] " + undoCommand.getClass().getName() + "
");
        return stringBuff.toString();
    }
}

6、測(cè)試類

package CeilingFan;

public class TestMain {
    public static void main(String[] args) {
        //實(shí)例化遙控器
        RemoteControlWithUndo remoteControl=new RemoteControlWithUndo();
        CeilingFan ceilingFan=new CeilingFan("臥室");
        //這里高中低速 關(guān)閉分別實(shí)例化
        CeilingFanHighCommand highCommand=new CeilingFanHighCommand(ceilingFan);
        CeilingFanMediumCommand mediumCommand=new CeilingFanMediumCommand(ceilingFan);
        CeilingFanLowCommand  lowCommand=new CeilingFanLowCommand(ceilingFan);
        CeilingFanOffCommand offCommand=new CeilingFanOffCommand(ceilingFan);
        
        //遙控器加載中速和高速的開啟和關(guān)閉方法
        remoteControl.setCommand(0, mediumCommand, offCommand);
        remoteControl.setCommand(1, highCommand, offCommand);
        //先以中速開啟吊扇
        remoteControl.onButtonWasPushed(0);
        //關(guān)閉吊扇
        remoteControl.offButtonWasPushed(0);
        //顯示插槽調(diào)用信息
        System.out.println(remoteControl.toString());
        //撤銷，會(huì)變?yōu)橹兴?        remoteControl.undoButtonWasPushed();
        
        remoteControl.onButtonWasPushed(1);
        System.out.println(remoteControl.toString());
        remoteControl.undoButtonWasPushed();    
    }
}

7、效果圖

其實(shí)命令模式還能用于宏命令，隊(duì)列請(qǐng)求，日志請(qǐng)求，命令模式我理解的很一般，往后我還會(huì)補(bǔ)充修改此篇內(nèi)容。

要點(diǎn)：
1：命令模式將發(fā)出請(qǐng)求的對(duì)象和執(zhí)行請(qǐng)求的對(duì)象解耦。
2：被解耦的兩者之間是通過命令對(duì)象進(jìn)行溝通的。命令對(duì)象封裝了接收者和一個(gè)或一組對(duì)象
3：調(diào)用者通過調(diào)用命令對(duì)象的execute方法發(fā)出請(qǐng)求，這會(huì)使得的接收者的動(dòng)作被調(diào)用。
4：命令可以支持撤銷動(dòng)作，實(shí)現(xiàn)一個(gè)undo方法來回到execute被執(zhí)行前的狀態(tài)。

感謝你看到這里，命令模式到這里就結(jié)束了，本人文筆隨便，若有不足或錯(cuò)誤之處望給予指點(diǎn)，90度彎腰~~~很快我會(huì)發(fā)布下一個(gè)設(shè)計(jì)模式的內(nèi)容，生命不息，編程不止！