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>
作者:Work Hard Work Smart
出处:http://www.cnblogs.com/linlf03/
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