Well, you need to have some relationship between the columns in different tables to know which row in one table combines with a row in another table, and then you basically do a join.
something like
SELECT a.col1, a.col2, b.col1, b.col2 FROM a, b WHERE a.col1=b.col2
Once you get a ResultSet from this query, iternate through it and do inserts in the new table. Best to use a PreparedStatement with SQL something like
INSERT INTO new_table(a_col1, a_col2, b_col1) VALUES (?,?,?)
and setting the parameters as you iterate through each row.
HTH
Danephew