I'm trying to use what I think may called an "inline update" against a
table in DB2.  My code basically looks like this:

PreparedStatement p=
    con.prepareStatement("select my_col from my_table where my_key=?",
                ResultSet.TYPE_FORWARD_ONLY,
                ResultSet.CONCUR_UPDATABLE);
p.setString(1, key);
ResultSet rs=p.executeQuery();
if(!rs.next()) {
    throw new SQLException("Not found: "+key);
}
String oldValue=rs.getString(1);
rs.updateString(1, newValue); // <-- problem here
rs.updateRow();

The problem is that the updateString method call throws a SQLException
that says "Column not updatable."  I have rights to perform the update,
because if I do a select statement then an update statement, it works.
Any ideas what's going on or how to fix it?  I've tried saying "select
... for update of my_col," but that doesn't work either.