Java Array HashCode实现 [英] Java Array HashCode implementation

问题描述

这很奇怪。一位同事询问了java中myArray.hashCode（）的实现。我以为我知道但后来我跑了几个测试。检查下面的代码。我注意到的奇怪的想法是，当我写第一个系统时，结果是不同的。请注意，它几乎就像报告内存地址并修改类移动了地址或其他内容。我以为我会分享。

This is odd. A co-worker asked about the implementation of myArray.hashCode() in java. I thought I knew but then I ran a few tests. Check the code below. The odd think I noticed is that when I wrote the first sys out the results were different. Note that it's almost like it's reporting a memory address and modifying the class moved the address or something. Just thought I would share.

int[] foo = new int[100000];
java.util.Random rand = new java.util.Random();

for(int a = 0; a < foo.length; a++) foo[a] = rand.nextInt();

int[] bar = new int[100000];
int[] baz = new int[100000];
int[] bax = new int[100000];
for(int a = 0; a < foo.length; a++) bar[a] = baz[a] = bax[a] = foo[a];

System.out.println(foo.hashCode() + " ----- " + bar.hashCode() + " ----- " + baz.hashCode() +  " ----- " + bax.hashCode());

// returns 4097744 ----- 328041 ----- 2083945 ----- 2438296
// Consistently unless you modify the class.  Very weird
// Before adding the comments below it returned this:
// 4177328 ----- 4097744 ----- 328041 ----- 2083945


System.out.println("Equal ?? " +
  (java.util.Arrays.equals(foo, bar) && java.util.Arrays.equals(bar, baz) &&
  java.util.Arrays.equals(baz, bax) && java.util.Arrays.equals(foo, bax)));

推荐答案

java.lang。数组 hashCode 方法继承自 Object ，这意味着哈希码取决于引用。要根据数组的内容获取哈希码，请使用 Arrays.hashCode 。

The java.lang.Array hashCode method is inherited from Object, which means the hashcode depends on the reference. To get the hashcode based on the content of the array use Arrays.hashCode.

请注意，虽然它的哈希码很浅实现。还有一个深度实现 Arrays.deepHashCode 。

Beware though its a shallow hashcode implementation. A deep implementation is also present Arrays.deepHashCode.

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