为什么在调用其方法（最佳实践或出于特定原因）之前将最终字段变量分配给本地副本？ [英] Why assign a final field variable to a local copy before calling its method (Best Practice or for a specific reason)?

问题描述

检查 ArrayBlockingQueue 的源代码时，我注意到在调用对象实例的任何方法之前，已将最终字段分配给局部变量。这是为了达到特定目的吗？

When checking the source code of ArrayBlockingQueue I noticed that before calling on any method of an object instance, a final field has been assigned to a local variable. Is this done to achieve a specific purpose?

public E peek() {
    final ReentrantLock lock = this.lock;
    lock.lock();
    try {
        return (count == 0) ? null : items[takeIndex];
    } finally {
        lock.unlock();
    }
}

推荐答案

那里是关于此处的讨论。基本上它是一种优化，允许更快地访问锁。即使this.lock是最终的，jvm仍然会在每次访问this.lock时进行字段查找，通过制作最终副本，它会稍快一点。

There is a discussion about that here. Basically it is an optimization, allowing quicker access to the lock. Even though this.lock is final, the jvm still does a field lookup every time this.lock is accessed, by making a final copy, it is slightly faster.

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