1️⃣概述

定义 : 允许一个对象在其内部状态改变时,改变它的行为;
类型 : 行为型;

2️⃣使用场景

一个对象存在多个状态(不同状态下行为不同)且状态可相互切换;

3️⃣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,减少相互间的依赖;
增加新的状态比较简单;

4️⃣缺点

状态多的业务场景导致类的数目增加,系统将会变得比较复杂;

5️⃣状态模式Coding

1 创建CourseVideoState抽象类

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 创建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 stop(){
        this.courseVideoState.stop();
    }

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

3 创建不同的状态类

/**
 * 暂停状态
 */
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);
    }
}

/**
 * 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);
    }
}

/**
 * 快进状态
 */
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);
    }
}

/**
 * 停止状态
 */
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");
    }
}

4 UML类图

5 编写测试类

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();
    }
}

6️⃣状态模式源码解析

JSF : javax.faces.lifecycle execute()