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https://issues.apache.org/jira/browse/COLLECTIONS-311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12663197#action_12663197
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Stephen Colebourne commented on COLLECTIONS-311:
------------------------------------------------
Javadoc from the JDK
"Note: Great care must be exercised if mutable objects are used as set
elements. The behavior of a set is not specified if the value of an object is
changed in a manner that affects equals comparisons while the object is an
element in the set. A special case of this prohibition is that it is not
permissible for a set to contain itself as an element. "
http://java.sun.com/j2se/1.5.0/docs/api/java/util/Set.html
While I understand that this caused you many difficulties, it is fundamentally
an invalid use of a Set (or Map key) to mutate the object after adding it.
> isEqualSet method in SetUtils could rehash the two input sets before it does
> the containsAll comparison
> -------------------------------------------------------------------------------------------------------
>
> Key: COLLECTIONS-311
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-311
> Project: Commons Collections
> Issue Type: Improvement
> Components: Set
> Affects Versions: 3.2
> Reporter: Michael Qiu
>
> Hey Guys
> I had an interesting problem recently where I was comparing 2 sets and the
> equals method was returning false... maybe it might be easier to understand
> if I explain using pseudo code:
> {code}
> set1.equals(set2) = false
> set1.get(0).equals(set2.get(0)) = true
> set1.get(1).equals(set2.get(1)) = true
> set1.get(0).hashCode() == set2.get(0).hashCode() = true
> set1.get(1).hashCode() == set2.get(1).hashCode() = true
> {code}
> So, objects in the two sets are equals, the hashCode of the objects in the
> two sets are equals, however the equals comparison at the set level was not
> equals.
> After some time, we figured out that the problem was that the object inside
> the set was getting modified after it was put into the set. So the new
> hashCode of the object has changed. However the bucket of the set that it's
> in hasn't changed. When another piece of code calls the contains method, it
> looks for the equivalent object in a bucket according to the new hashCode.
> When it doesn't find it, and it returns false.
> I would like to suggest that the SetUtils.isEqualSet method rehashes contents
> of the sets given in the parameters before it does the containsAll comparison
> to avoid the problem caused by this scenario.
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