JTree - JComboBox interaction

Question

I have a program that displays editable information for each node in a tree. I've run into a problem where a user may update the contents of a JComboBox and then click on a new node without saving their changes. If the information was just lost (as it is with a JTextField), I would have no problem, but the information is saved under the node that was just clicked. Below is an oversimplified example of my problem.
1) Click TreeNode 1, type something in the JComboBox, hit enter, and then click back and forth from TreeNode 2. Everything is as it should be.
2) Now restart the example (there is only a problem if the JComboBox is blank to begin with), and do the same thing without hitting enter.
In the actual program I have a custom TreeModel, a custom TreeSelectionListener, a custom TreeRenderer, etc. but nothing I've tried does any good (and I've tried so many different things, including creating a previousNode variable and an isBeingEditted variable, all to no avail).
The JComboBox and the automatic update both serve important purposes, so I'd like to keep that functionality. Any help would be greatly appreciated.
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.tree.*;
import java.awt.event.*;
import java.awt.*;
public class TreeComboBoxProblem extends JFrame {
    private JTree tree;
    private JLabel nodeName;
    private JComboBox nodeValue;
    public TreeComboBoxProblem(String name) {
        super(name);
        DefaultMutableTreeNode top = new DefaultMutableTreeNode(new TreeNode("TreeNode 0"));
        top.add(new DefaultMutableTreeNode(new TreeNode("TreeNode 1")));
        top.add(new DefaultMutableTreeNode(new TreeNode("TreeNode 2")));
        top.add(new DefaultMutableTreeNode(new TreeNode("TreeNode 3")));
        getContentPane().add( tree = new JTree(top), BorderLayout.NORTH );
        tree.addTreeSelectionListener( new TreeListener() );
        JPanel info = new JPanel();
        info.add( nodeName = new JLabel("TreeNode 0"));
        info.add( nodeValue = new JComboBox());
        nodeValue.setPreferredSize(new Dimension(102, 20));
        nodeValue.setEditable(true);
        nodeValue.addActionListener(new infoActionListener());
        getContentPane().add( info, BorderLayout.SOUTH );
    class TreeNode {
        String name;
        String value;
        public TreeNode(String name) {
            this.name = name;
            value = "";
        public String toString() {
            return name;
    protected class TreeListener implements TreeSelectionListener {
        public void valueChanged(TreeSelectionEvent e) {
            showInfo();
    public void showInfo() {
        TreeNode node = (TreeNode)((DefaultMutableTreeNode)tree.getSelectionPath().getLastPathComponent()).getUserObject();
        nodeName.setText(node.name);
        nodeValue.setSelectedItem(node.value);
    protected class infoActionListener implements ActionListener {
        public void actionPerformed(ActionEvent ae) {
            updateInfoSource();
    public void updateInfoSource() {
        TreeNode node = (TreeNode)((DefaultMutableTreeNode)tree.getSelectionPath().getLastPathComponent()).getUserObject();
        node.value = (String)nodeValue.getSelectedItem();
    public static void main(String[] args) {
        JFrame frame = new TreeComboBoxProblem("TreeComboBoxProblem");
        frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
        frame.pack();
        frame.setVisible( true );
}

Answer 1

This is another solution for the problem:
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTree;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.tree.DefaultMutableTreeNode;
public class TreeComboBoxProblem extends JFrame {
    private JTree tree;
    private JLabel nodeName;
    private JComboBox nodeValue;
    private TreeNode selectedNode;
    public TreeComboBoxProblem(String name) {
        super(name);
        DefaultMutableTreeNode top = new DefaultMutableTreeNode(new TreeNode("TreeNode 0"));
        top.add(new DefaultMutableTreeNode(new TreeNode("TreeNode 1")));
        top.add(new DefaultMutableTreeNode(new TreeNode("TreeNode 2")));
        top.add(new DefaultMutableTreeNode(new TreeNode("TreeNode 3")));
        getContentPane().add( tree = new JTree(top), BorderLayout.NORTH );
        tree.addTreeSelectionListener( new TreeListener() );
        JPanel info = new JPanel();
        info.add( nodeName = new JLabel("TreeNode 0"));
        info.add( nodeValue = new JComboBox(new String[] {}));       
        nodeValue.setPreferredSize(new Dimension(102, 20));
        nodeValue.setEditable(true);
        nodeValue.addActionListener(new infoActionListener());
        getContentPane().add( info, BorderLayout.SOUTH );
    class TreeNode {
        String name;
        String value;
        public TreeNode(String name) {
            this.name = name;
            value = "";
        public String toString() {
            return name;
    protected class TreeListener implements TreeSelectionListener {
        public void valueChanged(TreeSelectionEvent e) {
            showInfo();
    public void showInfo() {
        if (selectedNode != null)
            selectedNode.value = nodeValue.getEditor().getItem().toString();
        selectedNode = (TreeNode)((DefaultMutableTreeNode)tree.getSelectionPath().getLastPathComponent()).getUserObject();
        nodeName.setText(selectedNode.name);
        nodeValue.getEditor().setItem(selectedNode.value);
        nodeValue.setSelectedItem(selectedNode.value);
    protected class infoActionListener implements ActionListener {
        public void actionPerformed(ActionEvent ae) {
            updateInfoSource();
    public void updateInfoSource() {
        selectedNode.value = (String)nodeValue.getSelectedItem();
    public static void main(String[] args) {
        JFrame frame = new TreeComboBoxProblem("TreeComboBoxProblem");
        frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
        frame.pack();
        frame.setVisible( true );
}