设计模式-状态（State）模式

主要角色

职责

一个类有不同的状态，不同状态行为不同。状态之间可以切换。

类图

类关系示意图

代码

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();
}
---
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);
    }
}
---
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);
    }
}
---
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);
    }
}
---
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");
    }
}
---
public class CourseVideoContext {

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

    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();
    }
}

使用

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();
    }
}

技巧