java多线程。。。。。

Question

为什么结果会出现负的情况？ public class MyThreadTest { public static void main(String[] args) { MyThread m=new MyThread(); Thread t1=new Thread(m,"线程1"); Thread t2=new Thread(m,"线程2"); Thread t3=new Thread(m,"线程3"); Thread t4=new Thread(m,"线程4"); t1.start(); t2.start(); t3.start(); t4.start();} }class MyThread implements Runnable{ private int sum=10; private Object lock=new Object(); @Overridepublic void run() {     while(sum>0) {           //锁               synchronized (lock) {                   System.out.println(Thread.currentThread().getName()+" "+sum);                      sum--;                      }                      }                      }                  }

Answer 1

lock要用全局对象。不然各个线程各自减sum