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From "Thomas Neidhart (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (COLLECTIONS-416) ListUtils.removeAll() is very slow
Date Wed, 25 Jul 2012 21:40:34 GMT

    [ https://issues.apache.org/jira/browse/COLLECTIONS-416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13422638#comment-13422638
] 

Thomas Neidhart commented on COLLECTIONS-416:
---------------------------------------------

Added clarifying javadoc to the method in r1365784.
                
> 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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