Grading system.. using GUI and array

Basically, my problem is that I am not sure on how to set unlimited input arrays from user.. For now, the calculation only goes well if the user enters 6 subject exactly, but not if entered subject is less or more than 6.. Somehow, i want to make the input to be unlimited..

This is what I have so far

CGPA MAIN

import javax.swing.*;

public class CGPAMain extends JFrame
{
  public static void main(String[] args)
  {
    JFrame frame = new JFrame("GPA Calculation");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    MainPage panel = new MainPage();
    frame.getContentPane().add(panel);

    frame.pack();
    frame.setVisible(true);
  }
}

Mainpage

  import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;

    public class MainPage extends JPanel
    {
        //declare GUI elements
        private JLabel subjectLabel, cHoursLabel, gradeLabel;       
        private JTextField subject, cHours;
        private JButton addSubjectButton, calcGPAButton, clearAllButton;
        private JTextArea tArea;
        private JComboBox grade;

        //declare array to store and collect user input value
        String[] subjectArray = new String[6];                  
        String[] gradeArray = new String[6];
        int[] cHoursArray = new int[6];
        double[] gradeValue = { 4.00, 3.67, 3.33, 3.00, 2.67, 2.33, 2.00, 1.67, 1.33, 1.00, 0.00 };
        String[] gradeLetter= { "A",  "A-", "B+", "B",  "B-", "C+", "C",  "D",  "D-", "E",  "F"};                  


        public MainPage()
        {   
            setLayout (null);
            setPreferredSize (new Dimension(500, 500));
            setBackground (Color.orange); 

            //Properties of GUI elements
            subjectLabel = new JLabel ("Subject Name: ");                       
            subject = new JTextField (33);
            subject.addActionListener (new TempListener());

            gradeLabel = new JLabel ("Grade: ");
            grade = new JComboBox (gradeLetter); 
            grade.addActionListener (new TempListener());

            cHoursLabel = new JLabel ("Credit Hours: ");
            cHours = new JTextField (1);
            cHours.addActionListener (new TempListener());

            addSubjectButton = new JButton("Add Another Subject");
            addSubjectButton.addActionListener(new TempListener());
            calcGPAButton = new JButton("Calculate GPA");
            calcGPAButton.addActionListener(new TempListener());
            clearAllButton = new JButton("Clear All");
            clearAllButton.addActionListener(new TempListener());

            tArea = new JTextArea(5, 5);                
            tArea.setEditable(false);     

            add (subjectLabel);
            add (subject);
            add (gradeLabel);
            add (grade);
            add (cHoursLabel);
            add (cHours);
            add (addSubjectButton);
            add (calcGPAButton);
            add (clearAllButton);
            add (tArea);

            //Position of GUI elements
            subjectLabel.setBounds      (20, 20, 150, 20);              
            subject.setBounds           (120, 20, 350, 20);
            gradeLabel.setBounds        (20, 50, 50, 20);
            grade.setBounds             (120, 50, 50, 20);
            cHoursLabel.setBounds       (20, 80, 100, 20);
            cHours.setBounds            (120, 80, 50, 20);
            addSubjectButton.setBounds  (20, 120, 200, 30);
            calcGPAButton.setBounds     (300, 440, 175, 30);
            clearAllButton.setBounds    (20, 440, 120, 30);
            tArea.setBounds             (20, 170, 450, 250); 
        }


        private class TempListener implements ActionListener
        {
          //---------------------------------------------------------------------------
          //  Performs the conversion when the enter key is pressed in the text field.
          //---------------------------------------------------------------------------
            double tCrPoints = 0.00, tCrHours = 0.00, tGPA = 0.00;  
            String status; 

            public void actionPerformed(ActionEvent event)
            {
                if (event.getSource() == addSubjectButton)                   
                {
                    for (int i=0; i<6; i++)
                    {
                        subjectArray[i] = subject.getText();
                        gradeArray[i] = (String) grade.getSelectedItem();
                        cHoursArray[i] = Integer.parseInt(cHours.getText()); 
                    }

                    tArea.append (subject.getText() + "\t\t\t" + 
                                  grade.getSelectedItem() + "\t"  + 
                                  cHours.getText() + "\n"); 
                    subject.setText("");
                    cHours.setText(""); 
                }


                if (event.getSource() == calcGPAButton)   
                {
                    for (int i=0 ; i<gradeArray.length; i++)
                    {
                        for (int j=0; j<gradeLetter.length; j++)
                        {
                            if(gradeArray[i].equals(gradeLetter[j]))
                            {
                                tCrHours += cHoursArray[i]; 
                                tCrPoints += gradeValue[j] * cHoursArray[i];
                            }
                        }
                    }

                    tGPA = tCrPoints/tCrHours;

                    if (tGPA >= 2)
                        status = ("Pass");
                    else
                        status = ("Fail"); 

                    //Output for text area 
                    tArea.setText("Total Credit Points : " + tCrPoints + "\n" +
                                  "Total Credit Hours : " + tCrHours + "\n\n" + 
                                  "Grade Point Average (GPA) : " + tGPA + "\n" +
                                  "Status : " + status); 
                } 


                if (event.getSource() == clearAllButton)  
                {
                    tArea.setText("");
                    cHours.setText("");
                    grade.setSelectedIndex(0);
                    tCrHours = 0.00;
                    tCrPoints = 0.00;
                }


           }





        }
    }