设计模式——命令模式

2019-08-08  本文已影响0人  prik丶

《Head First 设计模式》 学习笔记,码云同步更新中

如有错误或不足之处,请一定指出,谢谢~

目录

设计原则
设计模式

命令模式(Command Pattern)

定义:
结构
分析

命令模式的本质是对命令进行封装,将命令发出和执行的责任分割开

优点:
缺点:
使用场景:
案例
/**
 * 命令接口
 **/
public interface Command {
    /**
     * 执行命令
     */
    public void execute();
    /**
     * 撤销命令
     */
    public void undo();
}
/**
 * 有7组开关的遥控器
 **/
public class RemoteControl {
    private static final int BUTTON_SIZE = 7;
    
    /**
     * 用数组记录遥控器上多个开关对应的命令
     */
    Command[] onCommands;
    Command[] offCommands;

    /**
     * 上一个命令
     */
    Command lastCommand;

    /**
     * 构造方法中初始化数组
     */
    public RemoteControl() {
        onCommands = new Command[BUTTON_SIZE];
        offCommands = new Command[BUTTON_SIZE];

        // 空对象
        Command noCommand = new NoCommand();

        for (int i = 0; i < BUTTON_SIZE; i++) {
            onCommands[i] = noCommand;
            offCommands[i] = noCommand;
        }
        lastCommand = noCommand;
    }

    /**
     * 往遥控器开关上设置命令
     */
    public void setCommand(int slot, Command onCommand, Command offCommand) {
        onCommands[slot] = onCommand;
        offCommands[slot] = offCommand;
    }

    /**
     * 开
     * @param slot
     */
    public void pushOnButton(int slot) {
        onCommands[slot].execute();
        lastCommand = onCommands[slot];
    }

    /**
     * 关
     * @param slot
     */
    public void pushOffButton(int slot) {
        offCommands[slot].execute();
        lastCommand = offCommands[slot];
    }

    /**
     * 撤销
     */
    public void pushUndoButton() {
        lastCommand.undo();
    }

    /**
     * 重写toString方法,给出遥控器说明书
     * @return
     */
    @Override
    public String toString() {
        StringBuffer stringBuffer = new StringBuffer();
        stringBuffer.append("\n-------- Remote Control --------\n");
        for (int i = 0; i < BUTTON_SIZE; i++) {
            stringBuffer.append("[slot " + i + "] " + onCommands[i].getClass().getName() + " / " + offCommands[i].getClass().getName() + "\n");
        }
        return stringBuffer.toString();
    }
}

家电

/**
 * 电灯
 **/
public class Light {

    public String tag;

    public Light(String tag) {
        this.tag = tag;
    }

    public void on() {
        System.out.println("the " + tag + " light is on...");
    }

    public void off() {
        System.out.println("the " + tag + " light is off...");
    }
}

/**
 * 电扇
 **/
public class ElectricFan {

    /**
     * 位置标记,区分哪里的电扇
     */
    private String tag;

    private int speed;

    public static final int OFF = 0;
    public static final int LOW = 1;
    public static final int MEDIUM = 2;
    public static final int HIGH = 3;

    public ElectricFan(String tag) {
        this.tag = tag;
    }

    public void speedHigh() {
        speed = HIGH;
        System.out.println("the " + tag + " fan is on high speed");
    }

    public void speedMedium() {
        speed = MEDIUM;
        System.out.println("the " + tag + " fan is on medium speed");
    }

    public void speedLow() {
        speed = LOW;
        System.out.println("the " + tag + " fan is on low speed");
    }

    public void turnOff() {
        speed = OFF;
        System.out.println("the " + tag + " fan is off");
    }

    public int getSpeed() {
        return speed;
    }
}

/**
 * 音响
 **/
public class Stereo {

    /**
     * 开机
     */
    public void on(){
        System.out.println("stereo is on...");
    }

    /**
     * 播放CD
     */
    public void playCD(){
        System.out.println("start playing CD...");
    }

    /**
     * 设置音量
     */
    public void setVolume(int volume){
        System.out.println("set the volume to " + volume);
    }

    /**
     * 关机
     */
    public void off() {
        System.out.println("stereo is off...");
    }
}

具体命令

/**
 * 空命令
 *
 * 空对象本身也可以被当做一种设计模式。
 * 可以用于当你不想返回一个有意义的对象时。
 * 遥控器在最初不可能设置了有意义的命令对象,
 * 使用空对象可以避免没必要的报错。
 **/
public class NoCommand implements Command {
    @Override
    public void execute() {
    }

    @Override
    public void undo() {
    }
}

/**
 * 打开电灯的命令
 **/
public class LightOffCommand implements Command {

    Light light;

    public LightOffCommand(Light light) {
        this.light = light;
    }

    @Override
    public void execute() {
        light.off();
    }

    @Override
    public void undo() {
        light.on();
    }
}

// 关闭电灯 略

/**
 * 电风扇 高风速 命令
 **/
public class ElectricFanSpeedHighCommand implements Command {

    ElectricFan fan;

    /**
     * 记录之前的风速
     */
    int prevSpeed;

    public ElectricFanSpeedHighCommand(ElectricFan fan) {
        this.fan = fan;
    }

    @Override
    public void execute() {
        // 记录风速
        prevSpeed = fan.getSpeed();
        fan.speedHigh();
    }

    /**
     * 撤销,恢复之前的风速
     */
    @Override
    public void undo() {
        if (prevSpeed == ElectricFan.HIGH) {
            fan.speedHigh();
        } else if (prevSpeed == ElectricFan.MEDIUM) {
            fan.speedMedium();
        } else if (prevSpeed == ElectricFan.LOW) {
            fan.speedLow();
        } else if (prevSpeed == ElectricFan.OFF) {
            fan.turnOff();
        }
    }
}

// 其他电扇命令 略

/**
 * 音响打开命令
 **/
public class StereoOffWithCdCommand implements Command {

    Stereo stereo;

    public StereoOffWithCdCommand(Stereo stereo) {
        this.stereo = stereo;
    }

    @Override
    public void execute() {
        stereo.off();
    }

    @Override
    public void undo() {
        stereo.on();
        stereo.playCD();
        stereo.setVolume(50);
    }
}

// 音响关闭命令 略

/**
 * 宏命令
 **/
public class MacroCommand implements Command {

    /**
     * 储存一组命令
     */
    Command[] commands;

    public MacroCommand(Command[] commands) {
        this.commands = commands;
    }

    /**
     * 一键全部执行
     */
    @Override
    public void execute() {
        for (int i = 0; i < commands.length; i++) {
            commands[i].execute();
        }
    }

    @Override
    public void undo() {
        for (int i = 0; i < commands.length; i++) {
            commands[i].undo();
        }
    }
}

测试类

/**
 * 遥控器测试
 **/
public class RemoteControlTest {
    public static void main(String[] args) {
        RemoteControl control = new RemoteControl();

        Light bedroomLight = new Light("bedroom");
        Light kitchenLight = new Light("kitchen");
        Stereo stereo = new Stereo();
        ElectricFan livingRoomFan = new ElectricFan("livingRoom");

        LightOnCommand bedroomLightOnCommand = new LightOnCommand(bedroomLight);
        LightOffCommand bedroomLightOffCommand = new LightOffCommand(bedroomLight);

        LightOnCommand kitchenLightOnCommand = new LightOnCommand(kitchenLight);
        LightOffCommand kitchenLightOffCommand = new LightOffCommand(kitchenLight);

        StereoOnWithCdCommand stereoOnWithCdCommand = new StereoOnWithCdCommand(stereo);
        StereoOffWithCdCommand stereoOffWithCdCommand = new StereoOffWithCdCommand(stereo);

        ElectricFanSpeedHighCommand livingRoomFanSpeedHighCommand = new ElectricFanSpeedHighCommand(livingRoomFan);
        ElectricFanOffCommand livingRoomFanOffCommand = new ElectricFanOffCommand(livingRoomFan);


        control.setCommand(0, bedroomLightOnCommand, bedroomLightOffCommand);
        control.setCommand(1, kitchenLightOnCommand, kitchenLightOffCommand);
        control.setCommand(2, stereoOnWithCdCommand, stereoOffWithCdCommand);

        control.setCommand(3, livingRoomFanSpeedHighCommand, livingRoomFanOffCommand);

        System.out.println(control.toString());

        // control.pushOnButton(1);
        // control.pushUndoButton();
        // control.pushOnButton(2);
        // control.pushOffButton(2);
        // control.pushUndoButton();

        // control.pushOnButton(3);
        // control.pushOffButton(3);
        // control.pushUndoButton();

        // 宏命令测试
        Command[] turnOnAllLightsArr = {bedroomLightOnCommand, kitchenLightOnCommand};
        Command[] turnOffAllLightsArr = {bedroomLightOffCommand, kitchenLightOffCommand};

        MacroCommand turnOnAllLights = new MacroCommand(turnOnAllLightsArr);
        MacroCommand turnOffAllLights = new MacroCommand(turnOffAllLightsArr);

        control.setCommand(4, turnOnAllLights, turnOffAllLights);

        control.pushOnButton(4);
        control.pushOffButton(4);
        control.pushUndoButton();
    }
}
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