[jira] [Commented] (HADOOP-9124) SortedMapWritable violates contract of Map interface for equals() and hashCode()

["Karthik Kambatla (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-9124?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13562258#comment-13562258 ] 

Karthik Kambatla commented on HADOOP-9124:
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On second thought, I think {{#equals()}} should verify if {{classToIdMap.keySet()}} and {{idToClassMap.values()}} should match for the two objects being compared. No?
                
> 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
>         Attachments: HADOOP-9124.patch, HADOOP-9124.patch, HADOOP-9124.patch, HADOOP-9124.patch, HADOOP-9124.patch, HADOOP-9124.patch
>
>
> 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
> --
> 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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