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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 21:44:34 GMT

    [ https://issues.apache.org/jira/browse/COLLECTIONS-416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13422644#comment-13422644
] 

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

Resolved as "Won't Fix". The user is responsible for using proper data structures as argument
to this method. This is also inline with the jdk whenever there are are methods that take
a Collection as input.
                
> 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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