Error message ResultSet.next not called

Question

I am a student learning java and am currently working on an assignement where I need to write jdbc programs that connect to an oracle database. The error message that I am getting is:
ResultSet.next was not called.
I do not know why I am getting this message. I wrote a simpler program to try to find the error, but I still got it again. Here's the part of the program:
ResultSet rset = stmt.executeQuery ("SELECT billing_id_seq.NEXTVAL Next_SeqNumber "+
                         "FROM Dual");
int sequenceNumber=rset.getInt("Next_SeqNumber");
     while(rset.next()){
System.out.println(sequenceNumber);
Any ideas would be helpful. Thanks very much!

Answer 1

I am not really sure if it is okay to post the whole program on this message board, but here it is:
import java.sql.*;     //Import Java's JDBC classes
public class CalculateEnrollFinalGrades {
public static void main(String[] args) {
//Invoke the processEnrollRecords() method
     processEnrollRecords();
} //end main()
// The following method issues a SQL SELECT statement to the database that returns the section_id
// and student_id for ALL rows from the enrollment_copy table. For each row received back in the
// result set, a call should be made to the updateEnrollFinalGrade() method. See below for
// information about what the that method does and what arguments it takes.
public static void processEnrollRecords() {
try {
Class.forName("oracle.jdbc.driver.OracleDriver"); // Load the Oracle JDBC driver
catch (java.lang.ClassNotFoundException e) {
System.out.println(e.getMessage());
try {
//Create the connection and statement objects
     Connection conn= DriverManager.getConnection("jdbc:oracle:oci8:@", "STUDENT","LEARN");
     Statement stmt=conn.createStatement();
//Execute a query in the CTA database which returns section_id and student_id for all
//rows of the enrollment_copy table
     int sectId=0;
     int studId=0;
     String sqlQuery="SELECT section_id, student_id "+
               "FROM enrollment_copy";
     ResultSet rset= stmt.executeQuery(sqlQuery);
//For each record returned in the ResultSet object, pass
//the current connection object along with each section_id and student_id as
//arguments to a method called updateEnrollFinalGrade()
     //while(rset.next()){
     sectId=rset.getInt("section_id");
     studId=rset.getInt("student_id");
     updateEnrollFinalGrade(conn, sectId, studId);
     //}//close while
//Close all resources before the program ends
     //conn.close();      //should this be kept open???
     stmt.close();
     rset.close();
     return;
catch (java.sql.SQLException e) { 
System.out.println(e.getMessage());
} // end processEnrollRecords()
// calculate a final_grade for the specified student
// and section, and then it updates the enrollment_copy table with the final_grade.
private static void updateEnrollFinalGrade(Connection conn_p, int sectionId_p, int studentId_p) {
try {
     Connection conn= DriverManager.getConnection("jdbc:oracle:oci8:@", "STUDENT","LEARN");
     Statement stmt=conn.createStatement();
     //query returns one row which is the final grade for the course for a particular student id and section.
     String sqlQuery2= "SELECT "+
     "ROUND(SUM((SUM(g.numeric_grade))/(COUNT(g.grade_type_code))*(gtw.percent_of_final_grade/100))) finGrade "+
     "FROM grade g, grade_type_weight gtw "+
     "where g.section_id=gtw.section_id AND g.grade_type_code=gtw.grade_type_code "+
     "AND g.student_id=? "+
     "AND g.section_id=? "+
     "GROUP BY gtw.percent_of_final_grade";
     PreparedStatement pstmt=conn.prepareStatement(sqlQuery2);
     pstmt.setInt(1, studentId_p);
     pstmt.setInt(2, sectionId_p);     
     ResultSet rsetGrade=pstmt.executeQuery();
     int finalGrade=rsetGrade.getInt("finGrade");
//Once the final_grade has been calculated, use a different PreparedStatement object to
//store it in the related enrollment_copy record. You need to use a Prepared
//Statement
     String sqlUpdate=      "Update enrollment_copy "+
                    "SET final_grade=? "+
                    "WHERE student_id=? AND section_id=?";
     PreparedStatement pstmtUpdate=conn.prepareStatement(sqlUpdate);
     pstmtUpdate.setInt(1,finalGrade);
     pstmtUpdate.setInt(2,studentId_p);
     pstmtUpdate.setInt(3,sectionId_p);
     pstmtUpdate.executeUpdate();
     pstmt.close();
     pstmtUpdate.close();          
     stmt.close();
     rsetGrade.close();
     return;
} // end try block
catch (java.sql.SQLException e) { 
System.out.println(e.getMessage());
} //end updateEnrollFinalGrade()
} //end CalculateEnrollFinalGrades
Thanks very mush for your help.