Java GUI Programming Help?

I've been stuck trying this for the past 4 hours, can't get anything to work. I could do this with check boxes and radio buttons no problem but I cant build any events that will calculate a total to display. ActionListeners are all void types so I can't insert an if else statement for it to calculate a total and return the value. I'm just stuck on the ListListener section. Can you please review and let me know how I can correct it? The instructions require us to use lists and combo boxes that have the included fields to calculate a total and display it in a read-only section without having to press any buttons. I've been trying to think of any possible way I could correct it but nothings helped. HUGE THANKS IN ADVANCE!

note: if you are trying to run this program yourself, you must delete the greeting panel i created as another class file.

import javax.swing.*;

import javax.swing.event.*;

import java.awt.*;

import java.awt.event.*;

public class ConfRegistration extends JFrame

{

private GreetingPanel banner;

private JPanel regPanel;

private JPanel optionalPanel;

private JPanel totalPanel;

private JComboBox regType;

private JList options;

private JList selectedOptions;

private JTextField regTotal;

private JTextField optTotal;

private JTextField total;

private JLabel regLabel;

private JLabel optLabel;

private JLabel totLabel;

private String[] combo = {"General Registration - $895.00 per person", "Student Registration - $495.00 per person"};

private String[] list = {"Introduction to E-commerce - $295.00", "The Future of the Web - $295.00", "Advanced" +

" Java Programming - $395.00", "Network Security - $395.00", "Opening Night Dinner - $30.00"};

private final double GENERAL_REG_FEE = 895.00;

private final double STUDENT_REG_FEE = 495.00;

public final double E_COMMERCE = 295.00;

public final double FUTURE_WEB = 295.00;

public final double JAVA = 395.00;

public final double NETWORK = 395.00;

public final double DINNER = 30.00;

public ConfRegistration()

{

setTitle("Conference Registration");

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

setLayout(new BorderLayout());

buildRegistrationPanel();

buildOptionalPanel();

buildTotalPanel();

banner = new GreetingPanel();

add(banner, BorderLayout.NORTH);

add(regPanel, BorderLayout.WEST);

add(optionalPanel, BorderLayout.EAST);

add(totalPanel, BorderLayout.SOUTH);

pack();

setVisible(true);

}

private void buildRegistrationPanel()

{

regPanel = new JPanel(); //create a panel to hold the combo box

regType = new JComboBox(combo); //create the combo box

regType.addActionListener(new ComboBoxListener()); //add action listener

regPanel.add(regType); //add combo box to panel

}

private void buildOptionalPanel()

{

optionalPanel = new JPanel(); //create a panel to hold the list

options = new JList(list); //create the list

selectedOptions = new JList(); //create a list to hold the selected options

options.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);

options.setVisibleRowCount(5);

options.setBorder(BorderFactory.createLineBorder(Color.BLACK, 1));

optionalPanel.add(options); //add list to panel

}

private void buildTotalPanel()

{

totalPanel = new JPanel(); //create a panel to hold the total

regLabel = new JLabel("Registration Subtotal: $");

regTotal = new JTextField(10);

optLabel = new JLabel("Optional Subtotal: $");

optTotal = new JTextField(10);

total = new JTextField(10);

totLabel = new JLabel("Total: $");

regTotal.setEditable(false);

optTotal.setEditable(false);

total.setEditable(false);

totalPanel.add(regLabel);

totalPanel.add(regTotal);

totalPanel.add(optLabel);

totalPanel.add(optTotal);

totalPanel.add(totLabel);

totalPanel.add(total);

}

private class ComboBoxListener implements ActionListener

{

public void actionPerformed(ActionEvent e)

{

int index;

double subtotal1 = 0.00;

index = regType.getSelectedIndex(); //get selected item and calculate subtotal

if (index == 0)

subtotal1 += GENERAL_REG_FEE;

else if (index == 1)

subtotal1 += STUDENT_REG_FEE;

regTotal.setText(Double.toString(subtotal1));

}

}

private class ListListeners implements ListSelectionListener

{

public void valueChanged(ListSelectionEvent e)

{

Object[] selections = options.getSelectedValues();

selectedOptions.setListData(selections);

double subtotal2 = 0.00;

if (options.isSelectedIndex(0))

subtotal2 = subtotal2 + E_COMMERCE;

if (options.isSelectedIndex(1))

subtotal2 = subtotal2 + FUTURE_WEB;

if (options.is(2))

subtotal2 = subtotal2 + JAVA;

if (options.isSelectedIndex(3))

subtotal2 = subtotal2 + NETWORK;