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From "Radim Kolar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8619) WritableComparator must implement no-arg constructor
Date Mon, 30 Jul 2012 09:49:35 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8619?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13424779#comment-13424779
] 

Radim Kolar commented on HADOOP-8619:
-------------------------------------

Java serialization do not capture constructor arguments into output stream. More detail about
protocol is here http://docs.oracle.com/javase/6/docs/platform/serialization/spec/protocol.html

If you create own constructor, java will not create default zero arg constructor http://xahlee.info/java-a-day/constructer.html
- section "Java Technicality: Default Constructors"
                
> WritableComparator must implement no-arg constructor
> ----------------------------------------------------
>
>                 Key: HADOOP-8619
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8619
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: io
>    Affects Versions: 3.0.0
>            Reporter: Radim Kolar
>             Fix For: 0.23.0, 2.0.0-alpha, 3.0.0
>
>         Attachments: writable-comparator.txt
>
>
> Because of reasons listed here: http://findbugs.sourceforge.net/bugDescriptions.html#SE_COMPARATOR_SHOULD_BE_SERIALIZABLE
> comparators should be serializable. To make deserialization work, it is required that
all superclasses have no-arg constructor. http://findbugs.sourceforge.net/bugDescriptions.html#SE_NO_SUITABLE_CONSTRUCTOR
> Simply add no=arg constructor to  WritableComparator.

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