多线程执行结果和预期不一样

Question

下面的程序为什么得不到稳定的想要的结果？

public class ThreadScopeShareData {

private static Map<Thread, Integer> threadData = new HashMap<Thread, Integer>();

public static void main(String[] args) {
    for (int i = 0; i < 2; i++) {

        new Thread(new Runnable() {

            @Override
            public void run() {
                int data = new Random().nextInt();
                System.out.println(Thread.currentThread().getName()
                        + " has put data :" + data);
                threadData.put(Thread.currentThread(), data);
                new A().get();
                new B().get();
            }
        }).start();
    }


}

static class A{
    public void get(){
        System.out.println("A from " + Thread.currentThread().getName()
                + " has put data :" + threadData.get(Thread.currentThread()));
    }
}

static class B{
    public void get(){
        System.out.println("B from " + Thread.currentThread().getName()
                + " has put data :" + threadData.get(Thread.currentThread()));
    }
}

}

结果：
Thread-0 has put data :-457543521
Thread-1 has put data :-1751454036
A from Thread-0 has put data :-457543521
A from Thread-1 has put data :null
B from Thread-1 has put data :null
B from Thread-0 has put data :-457543521

Answer 1

hashmap非线程安全