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From "Dusan Chromy (JIRA)" <>
Subject [jira] Commented: (COLLECTIONS-213) CollectionUtils API extension: algorithm methods accept an Iterator argument
Date Fri, 16 Jun 2006 15:51:30 GMT
    [ ]

Dusan Chromy commented on COLLECTIONS-213:

It just occured to me - in the middle of CollectionUtils-style programming :-) - that the
addition of the Iterator flavours methods will not only improve performance by avoiding the
unnecessary conversion from iterator to List, but also add the following benefit:

Imagine you have an input collection of "raw" objects which you transform to something else
by applying a Transformer. Now if you're only interested in finding a transformed object that
satisfies a given predicate, having an Iterator flavour of find/exists method will allow you
write a code like this:

Predicate predicate = ... ;
Transformer transformer = ... ;
CollectionUtils.find( IteratorUtils.transformedIterator( rawList.iterator(), transformer ),
predicate );

This is going to perform better than the workaround:

CollectionUtils.find( CollectionUtils.collect( rawList, transformer ), predicate );

Because the latter needs to apply the transformer to all elements in the list, even if the
first transformed element satisfies the predicate.

> CollectionUtils API extension: algorithm methods accept an Iterator argument
> ----------------------------------------------------------------------------
>          Key: COLLECTIONS-213
>          URL:
>      Project: Commons Collections
>         Type: New Feature

>     Reporter: Dusan Chromy
>  Attachments:,
> I just finished the Iterator additions to CollectionUtils, including test cases and I
am going to
> attach them to this issue very shortly (basically as soon as I figure out how attaching
in JIRA works :)
> At first I was thinking for a while whether CollectionUtils is a good place to accomodate
the methods with the
> new signature, until I noticed the collect method already accepts an Iterator argument.
> Following methods now accept an Iterator argument (besides collect):
> cardinality
> find
> forAllDo
> countMatches
> exists
> I also noticed cardinality used to throw a NPE if the collection argument was null.
> I see no reason why it should not return zero. The Iterator flavour does return zero
> and I also modified the Collection version to return zero (including Javadoc
> modification) for the sake of consistence.
> I stopped to think for a while before touching the method, but the fact
> that the Javadoc does not mention "may not be null" made me think the NPE is not thrown
> intentionally. And after all, cardinality(..) is nothing else than specialized countMatches(..),

> which returns 0 for null collection. However, feel free to reject the change to the cardinality(Object,Collection)
> method if you think otherwise.
> I worked on a fresh checkout from subversion and I just updated few minutes ago to make
sure I have modified
> the latest version. Anyway, please double-check before commiting the changes.
> Cheers,
> Dusan
> > I think that these methods would make useful additions to the API.
> > 
> > I don't have the time to do much collections work these days, but if you want to
code the methods with test cases and attach them to JIRA then that would be great.
> > 
> > Stephen
> > 
> > 
> > wrote:
> > 
> > > I've been using some algorithm methods from the CollectionUtils, for example
> > > find(Collection, Predicate)
> > > exists(Collection, Predicate)
> > > countMatches(Collection, Predicate)
> > > forAllDo(Collection, Closure)
> > >
> > > However, I would also like to be able to use these algorithms with an Iterator:
> > >
> > > find(Iterator, Predicate)
> > > exists(Iterator, Predicate)
> > > countMatches(Iterator, Predicate)
> > > forAllDo(Iterator, Closure)
> > >
> > > The obvious workaround is to use IteratorUtils.toList(Iterator), however this
comes at the cost of constructing a list object (an ArrayList presumably) which could be avoided,
as the Iterator itself is sufficient for the above algorithms to work.
> > >
> > > What do you think? Is there any reason not to provide the algorithms for an
Iterator? I personally think that the algorithms should have been there for Iterators in the
first place, because every collection is Iterable (or has an Iterator, prior to JDK 5.0).
> > >
> > > If noone is interested or has time to implement these changes, I can also contribute
to the project - but at the moment I just wanted to discuss the idea / check if this has been
already considered or planned.
> > >
> > > Best Regards,
> > >
> > > Dusan Chromy
> > 
> > 

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