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From "Thomas Neidhart (JIRA)" <j...@apache.org>
Subject [jira] [Closed] (COLLECTIONS-534) Performance bug in CollectionBag::retainAll
Date Fri, 27 Nov 2015 21:12:13 GMT

     [ https://issues.apache.org/jira/browse/COLLECTIONS-534?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Thomas Neidhart closed COLLECTIONS-534.
---------------------------------------

> Performance bug in CollectionBag::retainAll
> -------------------------------------------
>
>                 Key: COLLECTIONS-534
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-534
>             Project: Commons Collections
>          Issue Type: Bug
>          Components: Bag, Collection
>    Affects Versions: 4.0
>         Environment: Ubuntu 12.04
>            Reporter: Oswaldo Olivo
>              Labels: perfomance
>             Fix For: 4.1
>
>
> Hi,
> There seems to be a performance bug in the method retainAll in the CollectionBag class.
> The problem is that the code is checking containment over the parameter collection, which
could be expensive for some types of collections like ArrayLists.
> One solution could be to convert the Collection into a HashSet and check containment
in the HashSet.
>  If this is done, then running retainAll on a 1,000,000 collection would take less than
2 seconds instead of 27 mins, according to my experiments.
> ____________________________________________
> Here's a function to expose the bug:
>  public static void collectionBagRetainAllTest() {
> 	ArrayList<Integer> coll=new ArrayList<Integer>();
> 	for(int i=0;i<=1000000;++i)
> 	    coll.add(new Integer(i));
> 	TreeBag<Integer> treeBag=new TreeBag<Integer>(coll);
> 	CollectionBag<Integer> bag = new CollectionBag<Integer>(treeBag);
> 	bag.retainAll(coll);
>      }
> _____________________________________
> Here's a proposed patch:
>   public boolean retainAll(final Collection<?> coll) {
>         if (coll != null) {
>             boolean modified = false;
>             final Iterator<E> e = iterator();
> 	    HashSet<Object> set=new HashSet<Object>(coll);
>             while (e.hasNext()) {
>                 if (!set.contains(e.next())) {
>                     e.remove();
>                     modified = true;
>                 }
>             }
>             return modified;
>         } else {
>             // let the decorated bag handle the case of null argument
>             return decorated().retainAll(null);
>         }
>     }
> _____________________________________



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