How can I keep the selectedIndex of two JLists the same?

Question

I have two independant JLists. I have one button to add items from two textfields to the lists. I also have one button to remove the selected items from the lists. However because the items in both JLists are related I want to make sure the selected index of one is always equal to the selected index of the other. HOW!

Answer 1

OK, so here is the current code, there must be an easy way to do it, Swing gurus please help.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
public class ListDemo extends JFrame
                      implements ListSelectionListener {
    private JList list;
    private JList list2;
    private DefaultListModel listModel;
    private DefaultListModel listModel2;
    private static final String hireString = "Add";
    private static final String fireString = "Remove";
    private JButton fireButton;
    private JTextField employeeName;
    private JTextField percent;
    private JSlider per;
    public ListDemo() {
        super("ListDemo");
        listModel = new DefaultListModel();
        listModel.addElement("Alison Huml");
        listModel.addElement("Kathy Walrath");
        listModel.addElement("Lisa Friendly");
        listModel.addElement("Mary Campione");
        listModel2 = new DefaultListModel();
        listModel2.addElement("100");
        listModel2.addElement("80");
        listModel2.addElement("50");
        listModel2.addElement("10");
        //Create the list and put it in a scroll pane
        list = new JList(listModel);
        list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        list.setSelectedIndex(0);
        list.addListSelectionListener(this);
        JScrollPane listScrollPane = new JScrollPane(list);
        //Create the percentlist and put it in a scroll pane
        list2 = new JList(listModel2);
        list2.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        list2.setSelectedIndex(0);
        list2.addListSelectionListener(this);
        JScrollPane listScrollPane2 = new JScrollPane(list2);
        JButton hireButton = new JButton(hireString);
        hireButton.setActionCommand(hireString);
        hireButton.addActionListener(new HireListener());
        fireButton = new JButton(fireString);
        fireButton.setActionCommand(fireString);
        fireButton.addActionListener(new FireListener());
        employeeName = new JTextField(10);
        employeeName.addActionListener(new HireListener());
        String name = listModel.getElementAt(
                              list.getSelectedIndex()).toString();
        employeeName.setText(name);
        per = new JSlider(JSlider.HORIZONTAL, 0, 100, 50);
        per.setMajorTickSpacing(10);
        per.setPaintTicks(true);
        per.setPaintLabels(true);
        percent = new TextField(10);
        percent.setValue(new Integer(1));
        percent.addActionListener(new HireListener());
        String name2 = listModel2.getElementAt(
                              list2.getSelectedIndex()).toString();
        percent.setText(name2);
        //Create a panel that uses FlowLayout (the default).
        JPanel buttonPane = new JPanel();
        buttonPane.add(employeeName);
        buttonPane.add(per);
        buttonPane.add(hireButton);
        buttonPane.add(fireButton);
        Container contentPane = getContentPane();
        contentPane.add(listScrollPane, BorderLayout.CENTER);
        contentPane.add(listScrollPane2, BorderLayout.EAST);
        contentPane.add(buttonPane, BorderLayout.SOUTH);
    class FireListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            //This method can be called only if
            //there's a valid selection
            //so go ahead and remove whatever's selected.
            int index = list.getSelectedIndex();
            int index2 = list2.getSelectedIndex();
            listModel.remove(index);
            listModel2.remove(index2);
            int size = listModel.getSize();
            int size2 = listModel2.getSize();
            if (size == 0) {
            //Nobody's left, disable firing.
                fireButton.setEnabled(false);
            } else {
            //Adjust the selection.
                if (index == listModel.getSize())//removed item in last position
                    index--;
                list.setSelectedIndex(index);   //otherwise select same index
            if (size2 == 0) {
            //Nobody's left, disable firing.
                fireButton.setEnabled(false);
            } else {
            //Adjust the selection.
                if (index2 == listModel2.getSize())//removed item in last position
                    index2--;
                list2.setSelectedIndex(index2);   //otherwise select same index
    //This listener is shared by the text field and the hire button
    class HireListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            //User didn't type in a name...
            if (employeeName.getText().equals("")) {
                Toolkit.getDefaultToolkit().beep();
                return;
            //User didn't type in a percent...
            if (percent.getText().equals("")) {
                Toolkit.getDefaultToolkit().beep();
                return;
            int index = list.getSelectedIndex();
            int index2 = list2.getSelectedIndex();
            int size = listModel.getSize();
            int size2 = listModel2.getSize();
            //If no selection or if item in last position is selected,
            //add the new hire to end of list, and select new hire.
            if (index == -1 || (index+1 == size)) {
                listModel.addElement(employeeName.getText());
                list.setSelectedIndex(size);
            //Otherwise insert the new hire after the current selection,
            //and select new hire.
            } else {
                listModel.insertElementAt(employeeName.getText(), index+1);
                list.setSelectedIndex(index+1);
            //If no selection or if item in last position is selected,
            //add the new hire to end of list, and select new hire.
            if (index2 == -1 || (index2+1 == size2)) {
                listModel2.addElement(String.valueOf(per.getValue()));
                list2.setSelectedIndex(size2);
            //Otherwise insert the new hire after the current selection,
            //and select new hire.
            } else {
                listModel2.insertElementAt(String.valueOf(per.getValue()), index2+1);
                list2.setSelectedIndex(index2+1);
    public void valueChanged(ListSelectionEvent e) {
        if (e.getValueIsAdjusting() == false) {
            if (list.getSelectedIndex() == -1) {
            //No selection, disable fire button.
                fireButton.setEnabled(false);
                employeeName.setText("");
            } else {
            //Selection, update text field.
                fireButton.setEnabled(true);
                String name = list.getSelectedValue().toString();
                employeeName.setText(name);
            if (list2.getSelectedIndex() == -1) {
            //No selection, disable fire button.
                fireButton.setEnabled(false);
//                percent.setText("");
            } else {
            //Selection, update text field.
                fireButton.setEnabled(true);
                String name = list2.getSelectedValue().toString();
//                percent.setText(name);
    public static void main(String s[]) {
        JFrame frame = new ListDemo();
        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
        frame.pack();
        frame.setVisible(true);
}