狀態模式

定義：允許一個對象在其內部狀態改變時，改變它的行為
類型：行為型
適用場景：一個對象存在多個狀態（不同狀態下行為不同），且狀態可以相互轉換
優點：
- 將不同的狀態隔離
- 把各種狀態的轉換邏輯，分布到State的子類中，減少相互間依賴
- 增加新的狀態非常簡單
缺點：狀態多的業務場景導致類數目增加，系統變復雜
相關設計模式：
- 狀態模式和享元模式：有時候可以配合一起使用，可以使用享元模式在多個上下文角色之間共享這些狀態實例

Coding

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();
    }
}
/**
 * 課程視頻狀態抽象類
 */
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();

}
/**
 * 暫停狀態
 */
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("暫停播放課程視頻狀態");
    }

    @Override
    public void stop() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.STOP_STATE);
    }
}
/**
 * 播放狀態
 */
public class PlayState extends CourseVideoState {

    @Override
    public void play() {
        System.out.println("正常播放課程視頻狀態");
    }

    @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);
    }
}
/**
 * 快放狀態
 */
public class SpeedState extends CourseVideoState {

    @Override
    public void play() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.PLAY_STATE);
    }

    @Override
    public void speed() {
        System.out.println("快進播放課程視頻狀態");
    }

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

    @Override
    public void stop() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.STOP_STATE);
    }
}
/**
 * 停止狀態
 */
public class StopState extends CourseVideoState {

    @Override
    public void play() {
        super.courseVideoContext.setCourseVideoState(CourseVideoContext.PLAY_STATE);
    }

    @Override
    public void speed() {
        System.out.println("ERROR 停止狀態不能快進!!");
    }

    @Override
    public void pause() {
        System.out.println("ERROR 停止狀態不能暫停!!");
    }

    @Override
    public void stop() {
        System.out.println("停止播放課程視頻狀態");
    }
}

UML

測試

public class Test {
    public static void main(String[] args) {
        CourseVideoContext courseVideoContext = new CourseVideoContext();
        courseVideoContext.setCourseVideoState(new PlayState());

        System.out.println("當前狀態:" + courseVideoContext.getCourseVideoState().getClass().getSimpleName());
        courseVideoContext.pause();

        System.out.println("當前狀態:" + courseVideoContext.getCourseVideoState().getClass().getSimpleName());

        courseVideoContext.speed();

        System.out.println("當前狀態:" + courseVideoContext.getCourseVideoState().getClass().getSimpleName());

        courseVideoContext.stop();

        System.out.println("當前狀態:" + courseVideoContext.getCourseVideoState().getClass().getSimpleName());

        courseVideoContext.speed();
    }
}
========輸出=======
當前狀態:PlayState
當前狀態:PauseState
當前狀態:SpeedState
當前狀態:StopState
ERROR 停止狀態不能快進!!

源碼中的應用

在一些業務場景中可以用狀態模式，比如不同電商網站關于訂單扭轉的狀態，可以自己設置一個和業務場景非常契合的狀態機，還有一些比如我們的例子視頻狀態扭轉、辦公系統流程上的扭轉等等都是和具體的業務場景相關的，可以使用上狀態模式

posted @ 2024-01-31 12:20 wangzhilei 閱讀(28) 評論(0) 收藏舉報

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