状态模式

1.定义：允许一个对象在其内部状态改变时，改变它的行为。

2.类型：行为型

3.适用场景：一个对象存在多个状态(不同状态下行为不同)，且状态可相互转换。

4.优点：将不同的状态隔离，把各种状态的转换逻辑，分布到State的子类中，减少相互间依赖；
　　　   增加新的状态非常简单。

5.缺点：状态多的业务场景导致类数目增加，系统变得复杂

6.相关设计模式：享元模式

7.实例目录package

8.实例UML类图

9.代码

package com.geely.design.pattern.behavioral.state;

public abstract class CourseVideoState {
    protected CourseVideoContext courseVideoContext;

    public void setCourseVideoContext(CourseVideoContext courseVideoContext) {
        this.courseVideoContext = courseVideoContext;
    }

    public abstract void play();
    public abstract void speed();
    public abstract void pause();
    public abstract void stop();
}

package com.geely.design.pattern.behavioral.state;

public class PlayState extends CourseVideoState {
    @Override
    public void play() {
        System.out.println("正常播放课程视频状态");
    }

    @Override
    public void speed() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.SPEED_STATE);
    }

    @Override
    public void pause() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.PAUSE_STATE);
    }

    @Override
    public void stop() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.STOP_STATE);
    }
}

package com.geely.design.pattern.behavioral.state;

public class SpeedState extends CourseVideoState {
    @Override
    public void play() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.PLAY_STATE);
    }

    @Override
    public void speed() {
        System.out.println("快进播放课程视频状态");
    }

    @Override
    public void pause() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.PAUSE_STATE);
    }

    @Override
    public void stop() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.STOP_STATE);
    }
}

package com.geely.design.pattern.behavioral.state;

public class PauseState extends CourseVideoState {
    @Override
    public void play() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.PLAY_STATE);
    }

    @Override
    public void speed() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.SPEED_STATE);
    }

    @Override
    public void pause() {
        System.out.println("暂停播放课程视频状态");
    }

    @Override
    public void stop() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.STOP_STATE);
    }
}

package com.geely.design.pattern.behavioral.state;

public class StopState extends CourseVideoState {
    @Override
    public void play() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.PLAY_STATE);
    }

    @Override
    public void speed() {
        System.out.println("ERROR 停止状态不能快进！！");
    }

    @Override
    public void pause() {
        System.out.println("ERROR 停止状态不能暂停！！");
    }

    @Override
    public void stop() {
        System.out.println("停止播放课程视频状态");
    }
}

package com.geely.design.pattern.behavioral.state;

public class CourseVideoContext {
    private CourseVideoState courseVideoState;

    public final static PlayState PLAY_STATE = new PlayState();
    public final static SpeedState SPEED_STATE = new SpeedState();
    public final static PauseState PAUSE_STATE = new PauseState();
    public final static StopState STOP_STATE = new StopState();

    public CourseVideoState getCourseVideoState() {
        return courseVideoState;
    }

    public void setCourseVideoState(CourseVideoState courseVideoState) {
        this.courseVideoState = courseVideoState;
        this.courseVideoState.setCourseVideoContext(this);
    }

    public void play(){
        this.courseVideoState.play();
    }
    public void speed(){
        this.courseVideoState.speed();
    }
    public void stop(){
        this.courseVideoState.stop();
    }
    public void pause(){
        this.courseVideoState.pause();
    }
}

package com.geely.design.pattern.behavioral.state;

public class Test {
    public static void main(String[] args) {
        CourseVideoContext courseVideoContext = new CourseVideoContext();
        courseVideoContext.setCourseVideoState(new PlayState());

        System.out.println("当前状态：" + courseVideoContext.getCourseVideoState().getClass().getSimpleName());

        courseVideoContext.pause();
        System.out.println("当前状态：" + courseVideoContext.getCourseVideoState().getClass().getSimpleName());

        courseVideoContext.speed();
        System.out.println("当前状态：" + courseVideoContext.getCourseVideoState().getClass().getSimpleName());

        courseVideoContext.stop();
        System.out.println("当前状态：" + courseVideoContext.getCourseVideoState().getClass().getSimpleName());

        courseVideoContext.speed();
    }
}