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[docs fix]修正 hashCode() 方法的描述错误 #2001

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Snailclimb merged 1 commit into from
Apr 28, 2023
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[docs fix]修正 hashCode() 方法的描述错误 #2001

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13 changes: 12 additions & 1 deletion docs/java/basis/java-basic-questions-02.md
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Expand Up @@ -425,7 +425,18 @@ public boolean equals(Object anObject) {

![hashCode() 方法](https://oss.javaguide.cn/github/javaguide/java/basis/java-hashcode-method.png)

`hashCode()`定义在 JDK 的 `Object` 类中，这就意味着 Java 中的任何类都包含有 `hashCode()` 函数。另外需要注意的是： `Object` 的 `hashCode()` 方法是本地方法，也就是用 C 语言或 C++ 实现的，该方法通常用来将对象的内存地址转换为整数之后返回。
`hashCode()` 定义在 JDK 的 `Object` 类中，这就意味着 Java 中的任何类都包含有 `hashCode()` 函数。另外需要注意的是： `Object` 的 `hashCode()` 方法是本地方法，也就是用 C 语言或 C++ 实现的。

> 注:
>
> 该方法在 **Oracle OpenJDK8** 中默认是 "使用线程局部状态来实现 Marsaglia's xor-shift 随机数生成", 并不是 "地址" 或者 "地址转换而来", 不同JDK/VM可能不同
>
> 在 **Oracle OpenJDK8** 中有六种生成方式 (其中第五种是返回地址), 通过添加VM参数: -XX:hashCode=4 启用第五种。
>
> 参考源码:
>
> https://hg.openjdk.org/jdk8u/jdk8u/hotspot/file/87ee5ee27509/src/share/vm/runtime/globals.hpp, 1127行
> https://hg.openjdk.org/jdk8u/jdk8u/hotspot/file/87ee5ee27509/src/share/vm/runtime/synchronizer.cpp, 537行开始

```java
public native int hashCode();
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