[collections] CollectionUtils.getCardinalityMap JavaDoc

[Janek Bogucki <ya...@studylink.com>]

In CollectionUtils.getCardinalityMap the documentation notes the meaning of an entry that maps to null but I don't see how any such entry can exist in the returned map as all the keys in the map come from the collection parameter and will map to >=1. Have I missed something?

Re: [collections] CollectionUtils.getCardinalityMap JavaDoc

[Stephen Colebourne <sc...@btopenworld.com>]

Your logic makes sense to me ;-)
Stephen

----- Original Message -----
From: "Janek Bogucki" <ya...@studylink.com>
To: "Jakarta Commons Developers List" <co...@jakarta.apache.org>
Sent: Sunday, September 07, 2003 2:35 AM
Subject: [collections] CollectionUtils.getCardinalityMap JavaDoc


> In CollectionUtils.getCardinalityMap the documentation notes the meaning
of an entry that maps to null but I don't see how any such entry can exist
in the returned map as all the keys in the map come from the collection
parameter and will map to >=1. Have I missed something?
>
> >From CollectionUtils v 1.36
>
>     /**
>      * Returns a {@link Map} mapping each unique element in
>      * the given {@link Collection} to an {@link Integer}
>      * representing the number of occurences of that element
>      * in the {@link Collection}.
>      * An entry that maps to <tt>null</tt> indicates that the
>      * element does not appear in the given {@link Collection}.
>      */
>     public static Map getCardinalityMap(final Collection col) {
>         HashMap count = new HashMap();
>         Iterator it = col.iterator();
>         while(it.hasNext()) {
>             Object obj = it.next();
>             Integer c = (Integer)(count.get(obj));
>             if(null == c) {
>                 count.put(obj,new Integer(1));
>             } else {
>                 count.put(obj,new Integer(c.intValue() + 1));
>             }
>         }
>         return count;
>     }
>
>
> -Janek
>
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