selecting multiple values of other column basing on distinct values of column on same table

selecting multiple values of other column basing on distinct values of
column on same table

I am having a table in oracle my_table like
userid card_no
------- -------
111 A1
111 A5
112 A3
113 A4
111 A6
112 A8
113 A9
In my JSP page I want to show
-------------------------------------------------------------
user_id card numbers
------- ---------------------------------------------------
111 A1,A5,A6.
112 A3,A8
113 A4,A9
-------------------------------------------------------------
GROUP BY IS NOT GIVING RESULTS .