java线程安全Long,Java在下面的代码中java并发包里的AtomicLong为何不是线程安全的？...

大家都说AtomicLong是线程安全的&＃xff0c;以下的代码预期输出500&＃xff0c;可为什么实际执行时有时输出498、496&＃xff1f;是不是我的理解有问题导致哪个地方写错了&＃xff1f;

环境&＃xff1a;windows XP sp3&＃xff0c;jdk1.6.0_27

import java.util.concurrent.atomic.AtomicLong;

public class TestAtomicLong {

private final AtomicLong counter &＃61; new AtomicLong(0);

public AtomicLong getCounter() {

return counter;

}

public void test() {

for (int i &＃61; 0; i <500; i&＃43;&＃43;) {

new Thread(new Runnable() {

public void run() {

counter.getAndIncrement();

}

}).start();

}

}

public static void main(String[] args) {

TestAtomicLong obj &＃61; new TestAtomicLong();

obj.test();

System.out.println(obj.getCounter());//期望输出500&＃xff0c;可有时输出498、496

}

}