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https://issues.apache.org/jira/browse/COLLECTIONS-416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13414674#comment-13414674
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Thomas Neidhart commented on COLLECTIONS-416:
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Hi Adrian,
maybe this case is not as clear as for example COLLECTIONS-420. I think that
users should use the proper data structures for their use-cases and we should
be careful to not just mimick HashSet behavior regardless of what comes along.
If somebody provides a List to removeAll, he/she needs to be aware that this
will slow things down, and that a different data structure would be more
appropriate (IF it contains lots of data of course, when there are just 1 or 2
elements it makes not much of a difference).
Other people may have different opinions on this?
Thomas
> ListUtils.removeAll() is very slow
> ----------------------------------
>
> Key: COLLECTIONS-416
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-416
> Project: Commons Collections
> Issue Type: Bug
> Affects Versions: 3.2.1
> Environment: java 1.6.0_24
> Ubuntu 11.10
> Reporter: Adrian Nistor
> Attachments: Test.java, patch.diff
>
>
> Hi,
> I am encountering a performance problem in ListUtils.removeAll(). It
> appears in version 3.2.1 and also in revision 1355448. I attached a
> test that exposes this problem and a one-line patch that fixes it. On
> my machine, for this test, the patch provides a 217X speedup.
> To run the test, just do:
> $ java Test
> The output for the un-patched version is:
> Time is 5430
> The output for the patched version is:
> Time is 25
> As the patch shows, the problem is that
> "ListUtils.removeAll(Collection<E> collection, Collection<?> remove)"
> performs "remove.contains(obj)" for each element in "collection",
> which can be very expensive if "remove.contains(obj)" is expensive,
> e.g., when "remove" is a list.
> The one-line patch I attached puts the elements of "remove" in a
> HashSet (which has very fast "contains()"), if "remove" is not already
> a set:
> "if (!(remove instanceof java.util.Set<?>)) remove = new
> HashSet<Object>(remove);"
> Is this a bug, or am I misunderstanding the intended behavior? If so,
> can you please confirm that the patch is correct?
> Thanks,
> Adrian
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