如何从多线程类中正确获取静态变量？ [复制]

Question

假设我有这样的代码：

---

class A extends Thread {
    Thread t = new Thread();
    private static int id = 0;

    A(){
        id++;
        this.t.start();
    }

    private synchronized static int getId() { return id; }

    public void run() { System.out.println(getId()); }
}

public class Test throws InterruptedException {
    public static void main(String[] args) {
        A thread1 = new A();
        A thread2 = new A();
        try {
            thread1.t.join();
            thread2.t.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Main thread ends here");
    }
}

---

我期待这样的输出：

---

1
2

---

但是输出是：

---

2
2

---

我应该在这里做什么？感谢帮助。问。

Answer 1

对于这种情况，您应该使用AtomicInteger 而不是 int，并更改方法。

public class Test
{

    public static void main(String[] args) throws InterruptedException
    {
        final A thread1 = new A();
        final A thread2 = new A();
        try
        {
            thread1.join();
            thread2.join();
        }
        catch (final InterruptedException e)
        {
            e.printStackTrace();
        }
        Thread.sleep(1000);
        System.out.println("Main thread ends here");
    }

    public static class A extends Thread
    {
        private static final AtomicInteger id = new AtomicInteger(0);

        A()
        {
            start();
        }

        private synchronized int getID()
        {
            return id.get();
        }

        @Override
        public synchronized void run()
        {
            id.incrementAndGet();
            System.out.println(getID());
        }
    }
}