（a！= b）和（a！=（a = b））之间有什么区别？ [英] What is the difference between (a != b) and (a != (a = b)?

问题描述

在最近的问题，我们发现了以下代码：

In a recent question, we found the following piece of code:

// p, t, q and tail are Node<E> objects.
p = (p != t && t != (t = tail)) ? t : q;

忽略问题的上下文，我对以下行为感兴趣：

Omitting the context of the question, I am interested in the following behavior:

t != (t = tail)

考虑到这些是相同类型的对象，无论何种类型。这和之间有什么区别：

Considering those are the same type of objects, whatever the type. Is there any difference between this and:

t != tail

或者我在比较机制中缺少一些至关重要的东西？

Or am I missing something crucial in the comparison mechanism ?

编辑

如果有人想知道，可以在 ConcurrentLinkedQueue 类来自 java.util ，第352行。

If anyone wonders, this is found in the ConcurrentLinkedQueue class from java.util, line 352.

推荐答案

t != (t = tail)

相当于

oldt = t;
t = tail;
... oldt != t...

即。将 t 的原始值与 tail 进行比较，另外 t 被指定为 tail 的值。

i.e. the original value of t is compared to tail and in addition t is assigned the value of tail.

这是一个简短的写作方式

It's a short way of writing

if (t != tail) {
    t = tail;
}

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