行为型-状态模式

状态模式定义

允许一个对象在其内部状态发生改变时，改变它的行为

状态模式的适用场景

一个对象存在多个状态（不同状态下行为不同），且状态可以切换

状态模式的优点

• 将各个状态进行隔离
• 把各个状态的转换逻辑，分布到state的子类中，减少相互之间的依赖
• 增加新的状态比较简单

状态模式案例

实现一个视频播放状态案例

状态模式UML图

实现代码

package behaviorDesign.statusPattern;

/**
 * @author cuckooYang
 * @create 2020-08-16 21:24
 * @description 抽象状态类
 **/

public abstract class CourseVideoState {
    protected CourseVideoContext context;

    public void setContext(CourseVideoContext context) {
        this.context = context;
    }

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

package behaviorDesign.statusPattern;

/**
 * @author cuckooYang
 * @create 2020-08-16 21:24
 * @description
 **/

public class CourseVideoContext {
    //课程视频状态
    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;
        //设置课程视频上下文
        this.courseVideoState.setContext(this);
    }

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

package behaviorDesign.statusPattern;

/**
 * @author cuckooYang
 * @create 2020-08-16 21:27
 * @description
 **/

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 stop() {
        super.context.setCourseVideoState(CourseVideoContext.STOP_STATE);
    }

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

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

package behaviorDesign.statusPattern;

/**
 * @author cuckooYang
 * @create 2020-08-16 21:27
 * @description
 **/

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

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

    @Override
    public void pause() {
        System.out.println("ERROR 停止的视频不能暂停");
    }

    @Override
    public void speed() {
        System.out.println("ERROR 停止的视频不能加速");
    }
}

package behaviorDesign.statusPattern;

/**
 * @author cuckooYang
 * @create 2020-08-16 21:27
 * @description
 **/

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

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

    @Override
    public void pause() {
        System.out.println("暂停视频播放！！");
    }

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

package behaviorDesign.statusPattern;

import com.sun.scenario.effect.impl.sw.sse.SSEBlend_SRC_OUTPeer;

/**
 * @author cuckooYang
 * @create 2020-08-16 21:27
 * @description
 **/

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

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

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

    @Override
    public void speed() {
        System.out.println("加速视频播放！！");

    }
}

状态模式的缺点

状态多的业务场景导致类数量增加，系统变复杂，采用分而治之的方法，将状态进行划分不同的模块