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https://issues.apache.org/jira/browse/LANG-1813?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18054093#comment-18054093
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Gary D. Gregory edited comment on LANG-1813 at 1/24/26 12:56 PM:
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I think we have an actual bug because it's confusing to be different for these
edge cases from {{{}Arrays.hashCode(Object[]){}}}:
{code:java}
// JRE edge cases:
assertEquals(0, Arrays.hashCode((Object[]) null));
assertEquals(0, Arrays.hashCode((long[]) null));
assertEquals(1, Arrays.hashCode(ArrayUtils.EMPTY_OBJECT_ARRAY));
assertEquals(1, Arrays.hashCode(ArrayUtils.EMPTY_BOOLEAN_OBJECT_ARRAY));
{code}
See {{{}ArrayUtilsTest.testHashCode(){}}}.
An important difference with Arrays.hashCode() is that Arrays.hashCode()
doesn't do a deep hashCode() on the elements themselves.
was (Author: garydgregory):
I think we have an actual bug because it's confusing to be different for these
edge cases from {{Arrays.hashCode(Object[])}}:
{code:java}
// JRE edge cases:
assertEquals(0, Arrays.hashCode((Object[]) null));
assertEquals(0, Arrays.hashCode((long[]) null));
assertEquals(1, Arrays.hashCode(ArrayUtils.EMPTY_OBJECT_ARRAY));
assertEquals(1, Arrays.hashCode(ArrayUtils.EMPTY_BOOLEAN_OBJECT_ARRAY));
{code}
See {{ArrayUtilsTest.testHashCode()}}.
> `ArrayUtils#hashCode` Javadoc incorrectly states “null returns zero” (actual
> result is 629)
> -------------------------------------------------------------------------------------------
>
> Key: LANG-1813
> URL: https://issues.apache.org/jira/browse/LANG-1813
> Project: Commons Lang
> Issue Type: Bug
> Components: lang.*
> Reporter: Ivan Ponomarev
> Priority: Trivial
>
> Since commit 8c6294dd70f986088262a6b75a382cbc9e980543 (dated Jul 19, 2003),
> the Javadoc for {{org.apache.commons.lang3.ArrayUtils#hashCode(...)}} states
> that a {{null}} array input “returns zero”.
> However, this has never been true in practice: the method delegates to
> {{{}new HashCodeBuilder().append(array).toHashCode(){}}}, and
> {{HashCodeBuilder}} returns *629* for {{null}} input (with its default
> initial value and multiplier). This creates a long-standing discrepancy
> between documented and actual behavior.
> Given the age of the issue and the possibility that some legacy code may rely
> on the current behavior, changing the implementation to return 0 for {{null}}
> could be a breaking change. The safest resolution appears to be updating the
> Javadoc to match actual behavior (i.e., remove the “null returns zero”
> promise).
> Reproducer: the following test fails
> {code:java}
> @Test
> void testNullArrayHashCode() {
> // According to javadoc: "null returns zero"
> assertEquals(0, ArrayUtils.hashCode(null));
> }{code}
>
> Fix: https://github.com/apache/commons-lang/pull/1580
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