Java空检查 [英] Java null check

问题描述

我有一个 thread1 ：

if(object != null){
   object.play();
}

和另一个 thread2 可以随时将 null 写入对象。

and another thread2 that can write null into object reference at any time.

我会同时运行这些线程。我知道 null 后可以重写对象并且会抛出 NullPointerException 。在 NullPointerException 之后 thread2 重写 object 检查？

I will run these threads at same time. I know thread2 can rewrite object reference after the null check and that will throw NullPointerException. Is it possible for thread2 to rewrite object reference after NullPointerException check?

推荐答案

在NullPointerException检查后，thread2是否可以重写对象引用？ p>

Is it possible to for thread2 to rewrite object reference after NullPointerException check ?

绝对可以改变 object 的值，而 play（）方法正在执行，如果这是你的意思。

Absolutely - it could change the value of object while the play() method is executing, if that's what you mean. That wouldn't cause an error in itself.

请注意，没有同步或其他内存障碍，thread2可以更改 object 没有thread1注意到一个不确定的时间段。

Note that without synchronization or other memory barriers, thread2 could change the value of object without thread1 noticing for an indeterminate period of time.

很难说你应该做什么，没有任何其他知识的代码的更大的目的。

It's hard to say what you ought to do, without any other knowledge of the bigger aim of the code.

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