hashCode（）是如何在Java中实现的 [英] how is hashCode() implemented in Java

问题描述

hashCode （）实现了吗？

我的假设是它使用对象内存位置作为运行散列函数的初始数字（种子）。然而，事实并非如此。

我也看过哈希：它是如何在内部工作的？，但它不回答我的问题。

是我可以下载SDK ，但在我这样做之前，看看代码，也许别人已经知道它。

谢谢：）

编辑：
我知道它应该被覆盖，所以请尽量留在主题上：） >解决方案

当然，它是特定于实现的，但通常情况下，对象的哈希码将被延迟计算并存储在对象头中。奇怪的事情是使用头文件来保持它们的小，同时允许复杂的锁定算法。

在OpenJDK / Oracle JVM中，计算初始哈希代码的常用方法是基于内存地址在第一次请求时。对象在内存中移动，所以每次使用地址都不是一个好的选择。哈希码不是实际的地址 - 通常是8的倍数，这对于在哈希表中直接使用而言并不是很好，特别是在具有两种尺寸的情况下。注意标识哈希码不是唯一的。

HotSpot的构建时间选项始终使用零或使用安全随机数生成器（SRNG）进行测试。

How is hashCode() implemented?

My assumption is that it uses the object memory location as the initial number (the seed) on which it runs the hash function. However, this is not the case.

I've also looked at Hash : How does it work internally? but it does not answer my question.

Yes I could download the SDK, but before I do that and look at the code, perhaps someone else already has knowledge of it.

Thanks :)

EDIT: I know it should be overridden and such, so please try to stay on topic :)

解决方案

Of course it is implementation specific, but generally the hash code for an object will be computed lazily and stored in the object header. Odd things are done with headers to keep them small whilst allowing complex locking algorithms.

In the OpenJDK/Oracle JVM the usual method of computing the initial hash code is based on the memory address at the time of the first request. Objects move about in memory, so using the address each time would not be a good choice. The hash code isn't the actual address - that would typically be a multiple of eight which isn't great for using straight in a hash table particularly with a power of two size. Note identity hash codes are not unique.

HotSpot has build time options to always use zero or use a secure random number generator (SRNG) for testing purposes.

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