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https://issues.apache.org/jira/browse/HADOOP-7153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12998355#comment-12998355
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Nicholas Telford commented on HADOOP-7153:
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The tests fail in the QA because I attached the changes and the tests as
separate patches. Should I attach a single patch containing both to satisfy the
QA bot?
> 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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