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From "Joerg Schaible (JIRA)" <>
Subject [jira] Commented: (COLLECTIONS-266) Issue with MultiKey when serialized/deserialized via RMI
Date Fri, 14 Sep 2007 06:15:32 GMT


Joerg Schaible commented on COLLECTIONS-266:

IMHO the key simply violates the contract. Extract from Javadoc to Object.hashCode:

- If two objects are equal according to the equals(Object)  method, then calling the hashCode
method on each of the two objects must produce the same integer result

It also states:

- Whenever it is invoked on the same object more than once during an execution of a Java application,
the hashCode method must consistently return the same integer, provided no information used
in equals comparisons on the object is modified. This integer need not remain consistent from
one execution of an application to another execution of the same application.

Without testing it, but if you use this key not as part of a MultiKey, but of a HashMap directly,
you might get the same results.

> Issue with MultiKey when serialized/deserialized via RMI
> --------------------------------------------------------
>                 Key: COLLECTIONS-266
>                 URL:
>             Project: Commons Collections
>          Issue Type: Bug
>          Components: KeyValue
>    Affects Versions: 3.2
>            Reporter: Julien Buret
>            Priority: Minor
>             Fix For: 3.3
>         Attachments: COLLECTIONS-266.patch,,,,
> 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the hash code of the MultiKey is no longer valid, and you can't retreive the key in your Map.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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