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https://issues.apache.org/jira/browse/HADOOP-12973?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15230772#comment-15230772
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Colin Patrick McCabe commented on HADOOP-12973:
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Part of the reason I believe there should be a builder is because otherwise, we
have no way of adding new parameters in a backwards compatible way. For
example, if we want to add a Foobar parameter to the constructor, we can't do
that in a compatible fashion since the Factory is hard-coded to look for a
3-argument constructor with {{File, long, long}} by this code:
{code}
37 Constructor<? extends GetSpaceUsed> cons =
38 duKlass.getConstructor(File.class, long.class, long.class);
{code}
And if I accidentally implement a constructor with File, long, long that uses
those parameters for something else, weird stuff happens. For example, if I
have a constructor like this:
{{MyGetSpaceUsedSubclass(File birthdayMessage, long numberOfClowns, long
numberOfBirthdayCakes)}}, the factory will happily find it and pass it
arguments that make no sense. This can all be avoided by just passing the
Builder object to the constructor.
> make DU pluggable
> -----------------
>
> Key: HADOOP-12973
> URL: https://issues.apache.org/jira/browse/HADOOP-12973
> Project: Hadoop Common
> Issue Type: Sub-task
> Reporter: Elliott Clark
> Assignee: Elliott Clark
> Attachments: HADOOP-12973v0.patch, HADOOP-12973v1.patch,
> HADOOP-12973v10.patch, HADOOP-12973v2.patch, HADOOP-12973v3.patch,
> HADOOP-12973v5.patch, HADOOP-12973v6.patch, HADOOP-12973v7.patch,
> HADOOP-12973v8.patch, HADOOP-12973v9.patch
>
>
> If people are concerned about replacing the call to DU. Then an easy first
> step is to make it pluggable. Then it's possible to replace it with something
> while leaving the default alone.
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