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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