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From "Thomas Neidhart (JIRA)" <>
Subject [jira] [Resolved] (COLLECTIONS-420) CompositeCollection.containsAll() is very slow
Date Sun, 26 Aug 2012 21:27:07 GMT


Thomas Neidhart resolved COLLECTIONS-420.

    Resolution: Won't Fix

CompositeCollection is a decorator for existing collections. Operations shall not alter the
backing collections. To support a unified view on collections with a fast contains, users
should better use a CompositeSet and convert the collections to a set themselves.
> CompositeCollection.containsAll() is very slow
> ----------------------------------------------
>                 Key: COLLECTIONS-420
>                 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
> CompositeCollection.containsAll().  It appears in version 3.2.1 and
> also in revision 1355448.  I attached a test that exposes this problem
> and a patch that fixes it.  On my machine, for this test, the patch
> provides a 167X speedup.
> To run the test, just do:
> $ java Test
> The output for the un-patched version is:
> Time is 9192
> The output for the patched version is:
> Time is 54
> The problem is that 
> "CompositeCollection.containsAll(Collection<?> coll)" performs 
> "contains(item)" for each item in "coll", and "contains(item)"
> searches "item" in all collections in CompositeCollection.  This can
> be very slow if the collections in CompositeCollection have slow
> "contains()", e.g., when these collections are lists.
> The patch I attached puts the elements in each collection of
> CompositeCollection in a HashSet (which has very fast "contains()") if
> that collection is not already a set.  For efficiency, putting
> elements in several HashSet objects is performed lazily in the patch.
> 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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