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https://issues.apache.org/jira/browse/COLLECTIONS-266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12527381
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jburet edited comment on COLLECTIONS-266 at 9/14/07 1:23 AM:
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For Joerg: Here is the code of equals() and hashCode() methods of class Enum in
the sun 1.5 jvm:
public final boolean equals(Object other) {
return this==other;
}
public final int hashCode() {
return System.identityHashCode(this);
}
I think (and I hope ;) ) that the class Enum does not violate the hashCode
contract - but you can see that the same enum will not have the same hashCode
in two different jvms. The conclusion is : never serialize the hashCode (at
least for a modular class like MultiKey).
And the HashMap will work fine in this case, because in its writeObject() and
readObject() methods, the hashCode of each key is not serialized/deserialized:
only the key, the value and the size of the map are serialized: It works, I
have tested it.
Sorry for the multiple edits, but what I would like is to underline this
sentence of the hashCode contract : "This integer need not remain consistent
from one execution of an application to another execution of the same
application."
was (Author: jburet):
For Joerg: Here is the code of equals() and hashCode() methods of class
Enum in the sun 1.5 jvm:
public final boolean equals(Object other) {
return this==other;
}
public final int hashCode() {
return System.identityHashCode(this);
}
And the HashMap will work fine in this case, because in its writeObject() and
readObject() methods, the hashCode of each key is not serialized/deserialized:
only the key, the value and the size of the map are serialized: It works, I
have tested it.
Sorry for the multiple edits, but what I would like is to underline this
sentence of the hashCode contract : "This integer need not remain consistent
from one execution of an application to another execution of the same
application."
> 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
> Fix For: 3.3
>
> Attachments: COLLECTIONS-266.patch, MultiKey.java,
> TestCollections266.java, TestCollections266.java, TestCollections266.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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