getting nextval from query?

To create a primary key for one of my session beans within the ejbCreate(), I'm doing a the following.

...
query = "SELECT NEXTVAL('versions_seq')";

pstmt = dbConn.prepareStatement(query);

rs = pstmt.executeQuery();

rs.next();
num = (int) rs.getInt("last_value");

But as show by the exception below, this does not work. How do I get the nextval value out from this query? So it's an attribute ... but I'd still like to know how to get to it.

[Default] Exception = The column name last_value not found.
[BuildKit] TRANSACTION ROLLBACK EXCEPTION:null; nested exception is:
javax.ejb.EJBException

Any help much appreciated.