线程中更改全局变量的问题

线程中更改全局变量例子：
package 并发编程;


public class ConcurrencyTest {
public static  volatile long count = 100001;


public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
concurrency();
Thread.sleep(2000);
System.out.println(count);


}

private static synchronized void concurrency(){
Thread thread=new Thread(new Runnable(){


@Override
public synchronized void run() {
// TODO Auto-generated method stub
count=50;
//System.out.println(count);
}

});
thread.start();
//count=50;
         //System.out.println(count);
}


}
注意@@@
在线程中更改全局变量，只有在线程结束后（Thread.sleep()）才能更改，或许会是因为线程尚未开始就已经进行了输出结果。