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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-7153) MapWritable violates contract of Map interface for equals() and hashCode()
Date Wed, 23 Feb 2011 17:52:38 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12998470#comment-12998470
] 

Aaron T. Myers commented on HADOOP-7153:
----------------------------------------

Yes indeed. Please attach a single patch containing both the functional change and the associated
test.

> MapWritable violates contract of Map interface for equals() and hashCode()
> --------------------------------------------------------------------------
>
>                 Key: HADOOP-7153
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7153
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: io
>    Affects Versions: 0.21.0
>            Reporter: Nicholas Telford
>            Priority: Minor
>         Attachments: 7153-mapwritable-equality-test.diff, 7153-mapwritable-equality.diff
>
>
> o.a.h.io.MapWritable implements the java.util.Map interface, however it does not define
an implementation of the equals() or hashCode() methods; instead the default implementations
in java.lang.Object are used.
> This violates the contract of the Map interface which defines different behaviour for
equals() and hashCode() than Object does. More information here: http://download.oracle.com/javase/6/docs/api/java/util/Map.html#equals(java.lang.Object)
> The practical consequence is that MapWritables containing equal entries cannot be compared
properly. We were bitten by this when trying to write an MRUnit test for a Mapper that outputs
MapWritables; the MRUnit driver cannot test the equality of the expected and actual MapWritable
objects.

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