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状态模式

Posted on 2019-03-02 15:02  work hard work smart  阅读(196)  评论(0编辑  收藏  举报

一、定义

允许一个对象在内部状态改变时,改变它的行为。(不改变行为,只做状态的改变也是可以的)

类型:行为型

 

二、适用场景

1、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。

如订单状态,不同的订单状态,行为是不同的。如订单下单了之后,待付款状态,此时可以付款。

如订单,过了好多天,会自定关闭订单,关闭后是不能付款的。

 

三、状态模式-优点

1、将不同的状态隔离

2、把各种状态的转换逻辑,分布到State的子类中,减少相互间的依赖。

3、增加新的状态非常简单(新增类)

 

四、状态模式-缺点

1、状态多的业务场景导致类数目增加,系统变复杂

 

五、Coding

视频课程的状态有播放、暂停、快进、停止(无法快进)

1、CourseVideoState 类

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();
}

  

2、课程上下文 CourseVideoContext 类

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 pause(){
        this.courseVideoState.pause();
    }

    public   void stop(){
        this.courseVideoState.stop();
    }
    
}

  

3、播放状态

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);

    }
}

  

4、暂停状态 PauseState  

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);

    }
}

  

5、加速状态类

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);

    }
}

  

6、停止状态类

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");


    }
}

  

7、测试

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();

    }
}

  

结果:

当前状态:PlayState
当前状态:PauseState
当前状态:SpeedState
当前状态:StopState
Error停止状态不能快进

  

 

8、UML图

 

六、状态模式在源码中的使用(?没太明白)

1、jsf-api中

<dependency>
<groupId>com.sun.faces</groupId>
<artifactId>jsf-api</artifactId>
<version>1.2</version>
</dependency>