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From "Thomas Neidhart (JIRA)" <>
Subject [jira] [Commented] (COLLECTIONS-424) Surprising exception by CompositeSet in a situation where CompositeCollection works fine
Date Tue, 24 Jul 2012 20:56:34 GMT


Thomas Neidhart commented on COLLECTIONS-424:

Hi srirangadeepthi,

you can attach patches for this specific problem directly to the issue, there is no need to
assign the issue itself to you.

> Surprising exception by CompositeSet in a situation where CompositeCollection works fine
> ----------------------------------------------------------------------------------------
>                 Key: COLLECTIONS-424
>                 URL:
>             Project: Commons Collections
>          Issue Type: Bug
>          Components: Set
>    Affects Versions: 3.2.1
>         Environment: All environments
>            Reporter: Michael Pradel
> We have a method that uses a CompositeCollection. Here's a simplified version of it:
>   void m(CompositeCollection coll) {
>     coll.addComposited(new TreeBag());
>   }
> It works fine when the argument is a CompositeCollection, but it throws an exception
when the argument is a CompositeSet. E.g.:
>   m(new CompositeCollection());  // OK
>   m(new CompositeSet());         // IllegalArgumentException
> Although the exception is documented in CompositeSet, this behavior is very surprising.
Is there a way to have m() accept CompositeCollections without running into this exception?
The only solution that comes to my mind is to dynamically check the type of 'coll' in m(),
but this is a rather nasty work-around.
> A better solution may be to make the genericity of CompositeCollection explicit by adding
a type parameter:
>   class CompositeCollection<T extends Collection> {
>     void addComposited(T c) { /* .. */ }
>   }
>   class CompositeSet extends CompositeCollection<Set> {
>     @Override void addComposited(Set c) { /* .. */ }
>   }
> This way, users of CompositeCollection must choose the kind of collections that can be
composed and will not encounter surprises, such as the above.

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