Accessing values in an array of JComboBoxes

Question

Hello. I am building a program to calculate a user's GPA. This is a class assignment and so has some requirements I'm meeting.
There are two event handlers: One runs a loop to add course input lines; one calculates the GPA based on the inputs.
There are two related problems: When I instantiate JComboBoxes into two arrays (credits[] and grade[]) in the loop, the layout works but the calculate button only returns the values of credits[0] and grade[0] regardless of selection. When I instantiate the arrays outside the loop, the calculate button works but not the layout. I am at a complete loss. I'm posting the full code with comments. Sorry for it being very long.
package macdonnell_COMP228Lab4_Ex1;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class GPACalc extends JFrame {
     private String[] letterGrades = {"A+","A","B+","B","C+","C","D+","D","Fail"}; // Values to be used in combGrades
     private double[] gradePoints = {4.5,4.0,3.5,3.0,2.5,2.0,1.5,1.0,0};
     private String[] numberCourses = {"0","1","2","3","4","5","6","7","8"}; // Used to fill cbNumberCourses
     private String[] creditHours = {"1","2","3","4"}; //number of hours per week in the class
     private String[] numberGrades = {"90-100%","80-89%","75-79%","70-74%","65-69%","60-64%","55-59%","50-54%","0-49%"};
     private String[] combGrades = new String[9]; // Used to fill the JComboBox in grade[]
     //Arrays to hold JComboBoxes for Course Inputs
     private JComboBox[] credits = new JComboBox[8];
     private JComboBox[] grade = new JComboBox[8];
     private JLabel lblCreditHoursEarned = new JLabel("Credit Hours Earned: ");
     private JTextField txtCreditHoursEarned = new JTextField(5);
     private JLabel lblCurrentGPA = new JLabel("Current GPA: ");
     private JTextField txtCurrentGPA = new JTextField(5);
     private JLabel lblNumberCourses = new JLabel("Number of Courses: ");
     private JComboBox cbNumberCourses = new JComboBox(numberCourses); //ComboBox for users to select number of course inputs
     private JLabel lblNumber = new JLabel("Number: ");
     private JLabel lblCourseCode = new JLabel("Course Code: ");
     private JLabel lblCreditHours = new JLabel("Credit Hours: ");
     private JLabel lblGrade = new JLabel("Grade: ");
     private JLabel label;
     private JTextField coursCode;
     GridBagLayout gridBag;
     Container c;
     private JButton calculate = new JButton("Calculate");
     CalculateButtonHandler calculateButton = new CalculateButtonHandler();
     private JLabel lblYourGPA;
     public GPACalc(){
          for (int i = 0; i < combGrades.length; i++){
               combGrades[i] = letterGrades[i] + ": " + numberGrades;
          /* This block is used for instantiating the JComboBoxes in credits[] and grade[] outside the loop
          //Assign course input ComboBoxes to arrays
          credits[0] = new JComboBox(creditHours);
          credits[1] = new JComboBox(creditHours);
          credits[2] = new JComboBox(creditHours);
          credits[3] = new JComboBox(creditHours);
          credits[4] = new JComboBox(creditHours);
          credits[5] = new JComboBox(creditHours);
          credits[6] = new JComboBox(creditHours);
          credits[7] = new JComboBox(creditHours);
          grade[0] = new JComboBox(combGrades);
          grade[1] = new JComboBox(combGrades);
          grade[2] = new JComboBox(combGrades);
          grade[3] = new JComboBox(combGrades);
          grade[4] = new JComboBox(combGrades);
          grade[5] = new JComboBox(combGrades);
          grade[6] = new JComboBox(combGrades);
          grade[7] = new JComboBox(combGrades);
          gridBag = new GridBagLayout();
     c = getContentPane();
     c.setLayout(gridBag);
     // ROW 1
     GridBagConstraints Constr1 = new GridBagConstraints();
     Constr1.gridx = 0; //first column
     Constr1.gridy = 0; //first row
     Constr1.gridwidth = 2; //number of cells in the row that will be covered
     Constr1.gridheight = 1; //number of cells in the column
     Constr1.fill = GridBagConstraints.HORIZONTAL; //resize the component horizontally
     // add the text field
     gridBag.setConstraints(lblCreditHoursEarned, Constr1); //apply the constraints to the grid
     c.add(lblCreditHoursEarned);
     GridBagConstraints Constr2 = new GridBagConstraints();
     Constr2.gridx = 3; //second column
     Constr2.gridy = 0; //first row
     Constr2.gridwidth = 1; //number of cells in the row that will be covered
     Constr2.gridheight = 1; //number of cells in the column
     Constr2.fill = GridBagConstraints.HORIZONTAL; //resize the component horizontally
     // add the text field
     gridBag.setConstraints(txtCreditHoursEarned, Constr2); //apply the constraints to the grid
     c.add(txtCreditHoursEarned);
     GridBagConstraints Constr3 = new GridBagConstraints();
     Constr3.gridx = 5; //fourth column
     Constr3.gridy = 0; //first row
     Constr3.gridwidth = 1; //number of cells in the row that will be covered
     Constr3.gridheight = 1; //number of cells in the column
     Constr3.fill = GridBagConstraints.HORIZONTAL; //resize the component horizontally
     // add the text field
     gridBag.setConstraints(lblCurrentGPA, Constr3); //apply the constraints to the grid
     c.add(lblCurrentGPA);
     GridBagConstraints Constr4 = new GridBagConstraints();
     Constr4.gridx = 6; //fifth column
     Constr4.gridy = 0; //first row
     Constr4.gridwidth = 1; //number of cells in the row that will be covered
     Constr4.gridheight = 1; //number of cells in the column
     Constr4.fill = GridBagConstraints.HORIZONTAL; //resize the component horizontally
     // add the text field
     gridBag.setConstraints(txtCurrentGPA, Constr4); //apply the constraints to the grid
     c.add(txtCurrentGPA);
     //ROW 2
     GridBagConstraints Constr5 = new GridBagConstraints();
     Constr5.gridx = 5; //fourth column
     Constr5.gridy = 1; //second row
     Constr5.gridwidth = 1; //number of cells in the row that will be covered
     Constr5.gridheight = 1; //number of cells in the column
     Constr5.fill = GridBagConstraints.HORIZONTAL; //resize the component horizontally
     // add the text field
     gridBag.setConstraints(lblNumberCourses, Constr5); //apply the constraints to the grid
     c.add(lblNumberCourses);
     GridBagConstraints Constr6 = new GridBagConstraints();
     Constr6.gridx = 6; //fourth column
     Constr6.gridy = 1; //second row
     Constr6.gridwidth = 1; //number of cells in the row that will be covered
     Constr6.gridheight = 1; //number of cells in the column
     Constr6.fill = GridBagConstraints.HORIZONTAL; //resize the component horizontally
     // add the text field
     gridBag.setConstraints(cbNumberCourses, Constr6); //apply the constraints to the grid
     c.add(cbNumberCourses);
     //ROW 3
     GridBagConstraints Constr7 = new GridBagConstraints();
     Constr7.gridx = 0;
     Constr7.gridy = 2;
     Constr7.gridwidth = 1;
     Constr7.gridheight = 1;
     Constr7.fill = GridBagConstraints.HORIZONTAL;
     gridBag.setConstraints(lblNumber, Constr7);
     c.add(lblNumber);
     GridBagConstraints Constr8 = new GridBagConstraints();
     Constr8.gridx = 2;
     Constr8.gridy = 2;
     Constr8.gridwidth = 1;
     Constr8.gridheight = 1;
     Constr8.fill = GridBagConstraints.HORIZONTAL;
     gridBag.setConstraints(lblCourseCode, Constr8);
     c.add(lblCourseCode);
     GridBagConstraints Constr9 = new GridBagConstraints();
     Constr9.gridx = 4;
     Constr9.gridy = 2;
     Constr9.gridwidth = 1;
     Constr9.gridheight = 1;
     Constr9.fill = GridBagConstraints.HORIZONTAL;
     gridBag.setConstraints(lblCreditHours, Constr9);
     c.add(lblCreditHours);
     GridBagConstraints Constr10 = new GridBagConstraints();
     Constr10.gridx = 6;
     Constr10.gridy = 2;
     Constr10.gridwidth = 1;
     Constr10.gridheight = 1;
     Constr10.fill = GridBagConstraints.HORIZONTAL;
     gridBag.setConstraints(lblGrade, Constr10);
     c.add(lblGrade);
     //ROW 4 is built by the event handler cbNumberCourses.addItemListener at line 191; insert panel to hold ROW 4
     //ROW 5
     GridBagConstraints Constr11 = new GridBagConstraints();
     Constr11.gridx = 6;
     Constr11.gridy = 11;
     Constr11.gridwidth = 1;
     Constr11.gridheight = 1;
     Constr11.fill = GridBagConstraints.HORIZONTAL;
     gridBag.setConstraints(calculate, Constr11);
     c.add(calculate);
     //ROW 6 is added in the SubmitButtonHandler at line 242
     calculate.addActionListener(calculateButton);
     cbNumberCourses.addItemListener(
               new ItemListener(){
                    public void itemStateChanged(ItemEvent e){
                         for (int i = 0; i < cbNumberCourses.getSelectedIndex(); i++){
                              label = new JLabel(Integer.toString(i+1));
                              coursCode = new JTextField(10);
                              GridBagConstraints ConstrA = new GridBagConstraints();
                              ConstrA.gridx = 0;
                              ConstrA.gridy = i+4;
                              ConstrA.gridwidth = 1;
                              ConstrA.gridheight = 1;
                              ConstrA.fill = GridBagConstraints.HORIZONTAL;
                              gridBag.setConstraints(label, ConstrA);
                              c.add(label);
                              GridBagConstraints ConstrB = new GridBagConstraints();
                              ConstrB.gridx = 2;
                              ConstrB.gridy = i+4;
                              ConstrB.gridwidth = 1;
                              ConstrB.gridheight = 1;
                              ConstrB.fill = GridBagConstraints.HORIZONTAL;
                              gridBag.setConstraints(coursCode, ConstrB);
                              c.add(coursCode);
                              credits[i] = new JComboBox(creditHours);
                              GridBagConstraints ConstrC = new GridBagConstraints();
                              ConstrC.gridx = 4;
                              ConstrC.gridy = i+4;
                              ConstrC.gridwidth = 1;
                              ConstrC.gridheight = 1;
                              ConstrC.fill = GridBagConstraints.HORIZONTAL;
                              gridBag.setConstraints(credits[i], ConstrC);
                              c.add(credits[i]);
                              grade[i] = new JComboBox(combGrades);
                              GridBagConstraints ConstrD = new GridBagConstraints();
                              ConstrD.gridx = 6;
                              ConstrD.gridy = i+4;
                              ConstrD.gridwidth = 1;
                              ConstrD.gridheight = 1;
                              ConstrD.fill = GridBagConstraints.HORIZONTAL;
                              gridBag.setConstraints(grade[i], ConstrD);
                              c.add(grade[i]);
                         c.validate();
     private class CalculateButtonHandler implements ActionListener{
          public void actionPerformed(ActionEvent event){
               double creds, points, qualityPoints, gpa;
               double totalQualityPoints = 0;
               double totalCredits = 0;
               for (int i = 0; i < cbNumberCourses.getSelectedIndex(); i++){
                    System.out.println(i);
                    System.out.println(credits[i].getSelectedItem());
                    System.out.println(grade[i].getSelectedItem());
                    //creds = Double.parseDouble(creditHours[credits[i].getSelectedIndex()]);
                    creds = Double.parseDouble((String)credits[i].getSelectedItem());
                    points = gradePoints[grade[i].getSelectedIndex()];
                    totalCredits = totalCredits + creds;
                    qualityPoints = creds * points ;
                    totalQualityPoints = totalQualityPoints + qualityPoints;
                    System.out.println(creds);
                    System.out.println(points);
               gpa = totalQualityPoints / totalCredits;
               String yourGPA = "Your GPA is: " + gpa;
               lblYourGPA = new JLabel(yourGPA);
               GridBagConstraints Constr12 = new GridBagConstraints();
          Constr12.gridx = 3;
          Constr12.gridy = 12;
          Constr12.gridwidth = 1;
          Constr12.gridheight = 1;
          Constr12.fill = GridBagConstraints.HORIZONTAL;
          gridBag.setConstraints(lblYourGPA, Constr12);
          c.add(lblYourGPA);
          c.validate();
     public static void main(String[] args) {
          GPACalc mf = new GPACalc();
          mf.setSize(650,700);
          mf.setVisible( true ); // display frame

Answer 1

I changed the cbNumberCourses.addItemListener to an ActionListener. For whatever reason, this has fixed all my problems.