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https://issues.apache.org/jira/browse/DERBY-5035?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12995318#comment-12995318
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Knut Anders Hatlen commented on DERBY-5035:
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I took a quick look at the patch and noticed that many of the changed classes
inherited hashCode() methods from their super-classes, and that the inherited
methods satisfied the requirement x1.equals(x2) --> x1.hashCode() ==
x2.hashCode(), even when the sub-class had overridden the equals() method.
The equals() methods in many of the changed classes essentially just do:
return super.equals(other) && <some-other-condition>;
In these cases, if we decide to override the hashCode() method, we should use
super.hashCode() as a component when computing the new hash code. For example,
in TruncateOnCommit.java, the suggested new hashCode() method only returns 0 or
1, which wouldn't work very well in a hash table. If it had used
super.hashCode() there would be more variation in the returned hash values.
> [patch] equal objects should have equal hashcodes
> -------------------------------------------------
>
> Key: DERBY-5035
> URL: https://issues.apache.org/jira/browse/DERBY-5035
> Project: Derby
> Issue Type: Improvement
> Components: Network Server
> Affects Versions: 10.7.1.1
> Reporter: Dave Brosius
> Priority: Trivial
> Fix For: 10.8.0.0
>
> Attachments: equals_hashcode.diff
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> equal objects should have equal hashCodes otherwise they don't work correctly
> in hash collections.
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