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Re: proxy objects


hello guys

I may have a problem;

the context:

I store PersistentFacts(extends OzoneObject) in a HashMap of Lists.

here is a code extract from my application:

this is not working:

         Object[] objects = factsMap.get(factType);
         return (PersistentFact[])objects;
(throws a ClassCastException at the last line)

whereas this is working;

                 Object[] objects = factsMap.get(factType);
                 PersistentFact fact = (PersistentFact)objects[0];
                 PersistentFact[] facts = new PersistentFact[1];
                 facts[0] = fact;
                 return (PersistentFact[])objects;

could someone explain me why it is possible?



At 14:06 11/06/2001 +0200, you wrote:
>On Mon, 11 Jun 2001, Stan Pinte wrote:
> > hello,
> >
> > I have a question which doesn't seen to be documented:
> >
> > I have a database object (extending OzoneObject), which contains a 
> HashMap,
> > which contains Vectors, which contains other Database objects (extending
> > OzoneObject).
> >
> > Am I authorized to do this? I have the feeling that the HashMap and the
> > Vectors will have to be more or less "database-aware"...
>
>This should work without problems. The database objects which are stored 
>in the
>HashMap are proxies in reality. This is all the database wareness you need.
>
>There are pitfalls with the use of java2 collections however. One is that you
>cannot give an iterator of such a Collection to the outside of the datbase
>object that it belongs to. We discussed this some time ago. Anyway, IMO you
>should go ahead writing your code and come back with concrete
>questions/problems when they actually arise.
>
>
>Falko
>--
>______________________________________________________________________
>Falko Braeutigam                              mailto:falko@smb-tec.com
>SMB GmbH                                        http://www.smb-tec.com