命令模式-Command(Java实现)

命令模式-Command

将一个命令请求封装为一个对象, 这样就可以使用命令来修改目标对象的相关参数了.

本文的例子是, 狗主人(Master) 希望对狗狗发一些命令, 狗来进行响应, 以达到修改"参数"的作用.

比如, 发出让狗狗坐下, 吐舌头 等命令后...狗狗的参数就从站着变为了坐着, 从没伸出舌头变为了吐出舌头.

HandState枚举

public enum HandState {
    REACH("伸出爪子"), BACK("没伸出爪子");

    private String handState;

    HandState(String handState) {
        this.handState = handState;
    }

    @Override
    public String toString() {
        return handState;
    }
}

PostureState枚举

public enum PostureState {
    SITTING("坐着"), STANDING("站着");

    private String posture;

    PostureState(String posture) {
        this.posture = posture;
    }

    @Override
    public String toString() {
        return posture;
    }
}

TongueState枚举

public enum TongueState {
    SPIT("吐出舌头"), BACK("没伸出舌头");

    private String tongueState;

    TongueState(String tongueState) {
        this.tongueState = tongueState;
    }

    @Override
    public String toString() {
        return tongueState;
    }
}

Command接口

命令的抽象定义.

public interface Command {

    /**
     * 对dog执行命令
     */
    void execute(Dog dog);

    /**
     * 再来一遍刚刚那次execute(dog)
     */
    void undo();

    /**
     * 撤销刚刚那次execute(dog)
     */
    void redo();

    @Override
    String toString();

}

HandStateCommand类

握手命令

public class HandStateCommand implements Command {

    private Dog dog;

    @Override
    public void execute(Dog dog) {
        dog.setHandState(HandState.REACH);
        this.dog = dog;
    }

    @Override
    public void undo() {
        if (dog != null) {
            dog.setHandState(HandState.BACK);
        }
    }

    @Override
    public void redo() {
        if (dog != null) {
            dog.setHandState(HandState.REACH);
        }
    }

    @Override
    public String toString() {
        return "让狗伸出爪子的命令";
    }
}

PostureStateCommand类

站立/坐下姿势命令.

public class PostureStateCommand implements Command {

    private Dog dog;

    @Override
    public void execute(Dog dog) {
        dog.setPostureState(PostureState.SITTING);
        this.dog = dog;
    }

    @Override
    public void undo() {
        if (dog != null) {
            dog.setPostureState(PostureState.STANDING);
        }
    }

    @Override
    public void redo() {
        if (dog != null) {
            dog.setPostureState(PostureState.SITTING);
        }
    }

    @Override
    public String toString() {
        return "让狗坐下的命令";
    }
}

TongueStateCommand类

伸舌头/合上嘴 命令

public class TongueStateCommand implements Command {

    private Dog dog;

    @Override
    public void execute(Dog dog) {
        dog.setTongueState(TongueState.SPIT);
        this.dog = dog;
    }

    @Override
    public void undo() {
        if (dog != null) {
            dog.setTongueState(TongueState.BACK);
        }
    }

    @Override
    public void redo() {
        if (dog != null) {
            dog.setTongueState(TongueState.SPIT);
        }
    }

    @Override
    public String toString() {
        return "让狗吐出舌头的命令";
    }
}

Dog类

被命令的对象, 根据命令会改变Dog类的状态.

public class Dog {
    private HandState handState;
    private PostureState postureState;
    private TongueState tongueState;

    {
        handState = HandState.BACK;
        postureState = PostureState.STANDING;
        tongueState = TongueState.BACK;
    }

    public void setHandState(HandState handState) {
        this.handState = handState;
    }

    public void setPostureState(PostureState postureState) {
        this.postureState = postureState;
    }

    public void setTongueState(TongueState tongueState) {
        this.tongueState = tongueState;
    }

    @Override
    public String toString() {
        return "Dog{" +
                "handState=" + handState +
                ", postureState=" + postureState +
                ", tongueState=" + tongueState +
                '}';
    }

    public void printStatus() {
        System.out.println(this);
    }
}

Master类

由Master来施加命令来对Dog进行一些参数上的改变.

import java.util.Deque;
import java.util.LinkedList;

public class Master {

    private Deque<Command> undoStack = new LinkedList<>();
    private Command redo ;

    public Master() {
    }

    public void sendCommand(Command command, Dog dog) {
        System.out.printf("主人使用命令:<%s>\n", command);
        command.execute(dog);
        redo = command;
        undoStack.offerLast(command);
    }

    public void undoLastCommand() {
        if (!undoStack.isEmpty()) {
            Command previousSpell = undoStack.pollLast();
            redo = previousSpell;
            System.out.printf("主人撤回命令:<%s>\n", previousSpell);
            previousSpell.undo();
        }
    }

    public void redoLastCommand() {
        if (redo!=null) {
            undoStack.offerLast(redo);
            System.out.printf("再一次执行了命令:<%s>\n", redo);
            redo.redo();
        }
    }

    @Override
    public String toString() {
        return "狗的主人";
    }
}

Main

运行程序/ 场景模拟

public class Main {
    public static void main(String[] args) {
        Master master = new Master();

        Dog dog = new Dog();
        dog.printStatus();

        //开始命令狗, 站姿坐姿
        master.sendCommand(new PostureStateCommand(), dog);
        dog.printStatus();

        // 开始命令狗, 吐舌头
        master.sendCommand(new TongueStateCommand(), dog);
        dog.printStatus();

        master.redoLastCommand();
        dog.printStatus();

        master.undoLastCommand();
        dog.printStatus();

        master.redoLastCommand();
        dog.printStatus();

        master.undoLastCommand();
        dog.printStatus();

        // 开始命令狗, 伸爪子
        master.sendCommand(new HandStateCommand(), dog);
        dog.printStatus();

        master.redoLastCommand();
        dog.printStatus();

        master.undoLastCommand();
        dog.printStatus();
    }
}

运行结果如下: