synchronized 加锁Integer对象后，多线程还是会得到相同的数据

Question

 public class ThreadDemo implements Runnable  {

    public static volatile Integer a = 0;


    @Override
    public void run()  {

        try {
            while (a < 1000) {
                synchronized (a) {
                    a++;
                    System.out.println(Thread.currentThread() + ":"+ a);
                }
            }
        }catch (Exception e){}
    }
}

Answer 1

应该正常吧，19之后是21，两个线程各加了1