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https://issues.apache.org/jira/browse/COLLECTIONS-266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12526945
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Henri Yandell commented on COLLECTIONS-266:
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While creating the test I realized that the use case that found this problem
seems quite rare.
* MultiKey goes into Map.
* Map gets sent through serialize/deserialize.
* We have a new map, with a new multikey inside, with a new object inside that,
and the multikey has based its hashCode on the old address of the object and
not the new one.
If you dig that object out of the map, and then use it to try and get itself
back out of the map; then you've got a problem. So definitely a bug of sorts.
But how did you get access to the object in the first place? :)
In my unit test, I transfer the Map, then have to get the key back out of the
map to then use in a get request. ie:
MultiKey mk2 = (MultiKey) map2.keySet().iterator().next();
assertEquals(TWO, map2.get(mk2));
I find that the test passes for both the old code and your new code. Any idea
what I'm doing differently?
> Issue with MultiKey when serialized/deserialized via RMI
> --------------------------------------------------------
>
> Key: COLLECTIONS-266
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-266
> Project: Commons Collections
> Issue Type: Bug
> Components: KeyValue
> Affects Versions: 3.2
> Reporter: Julien Buret
> Priority: Minor
> Attachments: COLLECTIONS-266.patch, MultiKey.java
>
>
> This is because the hash code of MultiKey is calculated only once.
> So if the MultiKey is deserialized in an other jvm, and if one at least of
> the subkeys defines its hash code with System.identityHashCode() (for example
> all the enums does), then the hash code of the MultiKey is no longer valid,
> and you can't retreive the key in your Map.
> I fixed it by making the cached hash code field transient, and by
> recalculating the hash code during deserialization.
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