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https://issues.apache.org/jira/browse/LANG-839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13472431#comment-13472431
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Matt Benson commented on LANG-839:
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I don't know why {{BitSet}} never occurred to me; I guess because I haven't
used them much, if at all. It took me awhile to wrap my head around solving
the problem _at all_ (only creating one new array), so I'm perfectly happy
someone else found a way to make it (much) more efficient!
> ArrayUtils removeElements methods use unnecessary HashSet
> ---------------------------------------------------------
>
> Key: LANG-839
> URL: https://issues.apache.org/jira/browse/LANG-839
> Project: Commons Lang
> Issue Type: Improvement
> Components: lang.*
> Affects Versions: 3.1
> Reporter: Sebb
> Priority: Minor
> Fix For: 3.2
>
> Attachments: LANG-839.patch
>
>
> The removeElements() methods use a HashSet to collect the indexes that need
> removing.
> This requires creating Integer objects for each index, and the HashSet then
> has to be converted into an int[] array.
> It would be more efficient to store the entries in an actual int[] array.
> The maximum size of this is the length of the values array (or the length of
> the input array if that is shorter).
> The array must be truncated before calling the private removeAll() method;
> this can be done with Arrays.copyOf(x[], length).
> However, if the arrays are very large, and most of the values do not appear
> in the input, this might result in using more memory than the HashSet
> implementation.
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