commons-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Thomas Neidhart (JIRA)" <>
Subject [jira] [Commented] (COLLECTIONS-416) ListUtils.removeAll() is very slow
Date Sun, 15 Jul 2012 15:43:34 GMT


Thomas Neidhart commented on COLLECTIONS-416:

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?

> ListUtils.removeAll() is very slow
> ----------------------------------
>                 Key: COLLECTIONS-416
>                 URL:
>             Project: Commons Collections
>          Issue Type: Bug
>    Affects Versions: 3.2.1
>         Environment: java 1.6.0_24
> Ubuntu 11.10
>            Reporter: Adrian Nistor
>         Attachments:, 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

This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators:!default.jspa
For more information on JIRA, see:


View raw message