Such declaration like this

id int4 NOT NULL DEFAULT nextval('seq_group_id'::regclass)
and
CONSTRAINT i_group PRIMARY KEY (id)

give me the oportumity don't bother about unique value of id
and use another query.

INSERT INTO  groups(g_name) VALUES("new group");

I hope to find the same easy way in using ResultSet's objects (), i.e. to
forget about id in my code until it nessesary for me and not for jdbc.