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https://issues.apache.org/jira/browse/HADOOP-8549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13414867#comment-13414867
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madhukara phatak commented on HADOOP-8549:
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bq. Why can we hence not have a MapWritable(Class <? extends Map<Writable,
Writable>> mapType) that then instantiates the class for the field member
"instance", rather than a dev hacking like that?
AFAIK in M/R writable's are instantiated through default constructor, which
means the above constructor will not be called. So if I want to have a custom
Map instance implementation it has to be in read/write methods. Please correct
me if I am wrong :)
> Allow other implementation's of java.util.Map in MapWritable
> ------------------------------------------------------------
>
> Key: HADOOP-8549
> URL: https://issues.apache.org/jira/browse/HADOOP-8549
> Project: Hadoop Common
> Issue Type: Improvement
> Components: io
> Affects Versions: 2.0.0-alpha
> Reporter: madhukara phatak
> Assignee: madhukara phatak
> Priority: Minor
> Attachments: HADOOP-8549.patch
>
>
> Current implementation of MapWritable uses HashMap as Map implementation. But
> in some of the use cases we need other implementations of Map like
> LinkedHashMap,SortedMap.This jira changes visibility of 'instance' in
> MapWritable from private to protected which allows us to inject custom Map
> implementation through sub classing MapWritable .
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