It would really help if you would print the message and the stack trace of the exception you are getting. I can take a wild stab at it and point you to the documentation for java.sql.ResultSet:
A ResultSet object maintains a cursor pointing to its current row of data. Initially the cursor is positioned before the first row. The next method moves the cursor to the next row, and because it returns false when there are no more rows in the ResultSet object, it can be used in a while loop to iterate through the result set.