will Query.list() ever support generic collections?

hixson · **Joined:** Thu Sep 16, 2004 8:14 pm **Posts:** 27

In Hibernate 3.1 Query.list() returns a java.util.List.

I have this method:

Code:

public List<State> getAllStates() {
   Session session = HibernateUtil.getSession();
   Query query = session.createQuery("from State");
   query.setCacheable(true);
   return(query.list());
}

And Eclipse warns me about type safety in the return statement.

Even though I know that the query will never contain anything but State objects it would be nice if Query would return a List<State>.
Are there plans to implement that?

emmanuel · **Posted:** Fri Oct 14, 2005 5:51 am

This is not really possible the way the API is defined. You'd have to pass the returned class as a parameter of query.
The proper solution in your case is to actually cast the List into List<Blah> when returning it.

cbredesen · **Posted:** Fri Oct 14, 2005 8:12 am

You can silence Eclipse by using this annotation, since you're always going to have a safe cast:

Code:

@SuppressWarnings("unchecked")

-Chris

hixson · **Joined:** Thu Sep 16, 2004 8:14 pm **Posts:** 27

emmanuel wrote:

The proper solution in your case is to actually cast the List into List<Blah> when returning it.

When I change the return statement to:

Code:

return((List<State>)query.list());

Eclipse shows this warning:

Type safety: The cast from List to List<State> is actually checking against the erased type List

Mahoney · **Joined:** Fri Oct 14, 2005 11:40 am **Posts:** 7

If you really want to avoid the warnings, and you don't want to suppress them, the only way to do it is to copy the results of Query.list() manually into a new List<State>:

Quote:

List results = query.list();
List<State> newResults = new ArrayList<State>();
for (Object o : results) {
newResults.add((State) o);
}
return newResults;

That's the only "safe" way to do it as that's the only way that will guarantee that the resulting List<State> only contains State objects.

The reason you have to get the warnings is that at runtime a List and a List<State> object are both actually just plain List objects. So if query.list() returned a List ontaining anything other than State objects, the cast to List<State> would not cause any exception to be thrown - the program would continue fine, because no type checking of generics is done at runtime. Which might make debugging it difficult in future as you suddenly get a class cast exception popping up somewhere else in the program seemingly at random.

Of course you know that query.list() will only return State objects - but the compiler, and hence Eclipse, can't know that. Just suppress the warning - it has done its job, which is to ask you whether you are certain that the cast is valid.