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From "Patrick Hunt (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-9124) SortedMapWritable violates contract of Map interface for equals() and hashCode()
Date Sat, 08 Dec 2012 00:57:20 GMT
Patrick Hunt created HADOOP-9124:
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             Summary: SortedMapWritable violates contract of Map interface for equals() and
hashCode()
                 Key: HADOOP-9124
                 URL: https://issues.apache.org/jira/browse/HADOOP-9124
             Project: Hadoop Common
          Issue Type: Bug
          Components: io
    Affects Versions: 2.0.2-alpha
            Reporter: Patrick Hunt
            Priority: Minor


This issue is similar to HADOOP-7153. It was found when using MRUnit - see MRUNIT-158, specifically
https://issues.apache.org/jira/browse/MRUNIT-158?focusedCommentId=13501985&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13501985

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o.a.h.io.SortedMapWritable 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 SortedMapWritables 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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