Integration

I don't understand why when I do a simple query "Select count(*) From ...." and get use the EntityManager my code is something like this:
getEntityManager().createNativeQuery(sql).getSingleResult()

and what I get is a Vector object that has inside a BigDecimal object. I wonder how portable this is if I use hibernate. I bought a book that was written by a couple of guys from Oracle and their example returns a Object array instead of a Vector even when getResultList() function is called.

I can't find any documentation where it indicates what is returned from getSingleResult() and getResultList().

Any help from any gurus are most welcomed....