标签：void System 与逸出 states 安全 线程 new public out

1. 逸出

① private对象的逸出

/**
 * 描述：     发布逸出
 */
public class MultiThreadsError3 {

    private Map<String, String> states;

    public MultiThreadsError3() {
        states = new HashMap<>();
        states.put("1", "周一");
        states.put("2", "周二");
        states.put("3", "周三");
        states.put("4", "周四");
    }

    public Map<String, String> getStates() {
        return states;
    }

    public Map<String, String> getStatesImproved() {
        return new HashMap<>(states);
    }

    public static void main(String[] args) {
        MultiThreadsError3 multiThreadsError3 = new MultiThreadsError3();
        Map<String, String> states = multiThreadsError3.getStates();
        System.out.println(states.get("1"));
        states.remove("1");
        System.out.println(states.get("1"));

        System.out.println(multiThreadsError3.getStatesImproved().get("1"));
        multiThreadsError3.getStatesImproved().remove("1");
        System.out.println(multiThreadsError3.getStatesImproved().get("1"));

    }
}

② 还未完成初始化就将对象提供给外界 - 初始化未完毕，就this赋值

/**
 * 描述：     初始化未完毕，就this赋值
 */
public class MultiThreadsError4 {

    static Point point;

    public static void main(String[] args) throws InterruptedException {
        new PointMaker().start();
//        Thread.sleep(10);
        Thread.sleep(105);
        if (point != null) {
            System.out.println(point);
        }
    }
}

class Point {

    private final int x, y;

    public Point(int x, int y) throws InterruptedException {
        this.x = x;
        MultiThreadsError4.point = this;
        Thread.sleep(100);
        this.y = y;
    }

    @Override
    public String toString() {
        return x + "," + y;
    }
}

class PointMaker extends Thread {

    @Override
    public void run() {
        try {
            new Point(1, 1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

③ 还未完成初始化就将对象提供给外界 - 注册监听器

/**
 * 描述：     观察者模式
 */
public class MultiThreadsError5 {

    int count;

    public MultiThreadsError5(MySource source) {
        source.registerListener(new EventListener() {
            @Override
            public void onEvent(Event e) {
                System.out.println("\n我得到的数字是" + count);
            }

        });
        //do other thing
        for (int i = 0; i < 10000; i++) {
            System.out.print(i);
        }
        count = 100;
    }

    public static void main(String[] args) {
        MySource mySource = new MySource();
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                mySource.eventCome(new Event() {
                });
            }
        }).start();
        MultiThreadsError5 multiThreadsError5 = new MultiThreadsError5(mySource);
    }

    static class MySource {

        private EventListener listener;

        void registerListener(EventListener eventListener) {
            this.listener = eventListener;
        }

        void eventCome(Event e) {
            if (listener != null) {
                listener.onEvent(e);
            } else {
                System.out.println("还未初始化完毕");
            }
        }

    }

    interface EventListener {

        void onEvent(Event e);
    }

    interface Event {

    }
}

④ 构造函数中运行线程

/**
 * 描述：     构造函数中新建线程
 */
public class MultiThreadsError6 {

    private Map<String, String> states;

    public MultiThreadsError6() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                states = new HashMap<>();
                states.put("1", "周一");
                states.put("2", "周二");
                states.put("3", "周三");
                states.put("4", "周四");
            }
        }).start();
    }

    public Map<String, String> getStates() {
        return states;
    }

    public static void main(String[] args) throws InterruptedException {
        MultiThreadsError6 multiThreadsError6 = new MultiThreadsError6();
        Thread.sleep(1000);
        System.out.println(multiThreadsError6.getStates().get("1"));
    }
}

2. 如何解决逸出

① 对于private对象返回副本
② 工厂模式解决还未完成初始化就将对象提供给外界

/**
 * 描述：     用工厂模式修复刚才的初始化问题
 */
public class MultiThreadsError7 {

    int count;
    private EventListener listener;

    private MultiThreadsError7(MySource source) {
        listener = new EventListener() {
            @Override
            public void onEvent(MultiThreadsError5.Event e) {
                System.out.println("\n我得到的数字是" + count);
            }

        };
        for (int i = 0; i < 10000; i++) {
            System.out.print(i);
        }
        count = 100;
    }

    public static MultiThreadsError7 getInstance(MySource source) {
        MultiThreadsError7 safeListener = new MultiThreadsError7(source);
        source.registerListener(safeListener.listener);
        return safeListener;
    }

    public static void main(String[] args) {
        MySource mySource = new MySource();
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                mySource.eventCome(new MultiThreadsError5.Event() {
                });
            }
        }).start();
        MultiThreadsError7 multiThreadsError7 = new MultiThreadsError7(mySource);
    }

    static class MySource {

        private EventListener listener;

        void registerListener(EventListener eventListener) {
            this.listener = eventListener;
        }

        void eventCome(MultiThreadsError5.Event e) {
            if (listener != null) {
                listener.onEvent(e);
            } else {
                System.out.println("还未初始化完毕");
            }
        }

    }

    interface EventListener {

        void onEvent(MultiThreadsError5.Event e);
    }

    interface Event {

    }
}

3. 各种需要考虑线程安全的问题

4. 上下文切换，内存同步

标签：void,System,与逸出,states,安全,线程,new,public,out
来源： https://blog.csdn.net/weixin_43907800/article/details/110881919

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