About to use my tree for some firewood :o(

Question

I was wondering if someone could maybe clue me into a problem that I am having with my DefaultMutableTree. See, I call a recursive method to get the file system of the computer, which is what is added to the tree. So the user is looking at a tree structure of the file system of their computer. My problem is that when I compile and run my program the tree shows up fine, with no hitches. I have given my code to other friends, and for some of them it does not show up, and throws a null pointer exception at the internal interface of this recursive method. I was wondering what might be causing this? My friends that have problems with the code are running either WIN XP, or Mac OS 10.1.4. Here is the code for the initialization of the tree (This will look ugly on the post, so I would hope that you would take the time to copy and paste this into your editor :D)
//code start.
import java.io.*;
import java.io.File;
import java.lang.*;
import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.event.*;
import java.beans.*;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.event.TreeSelectionListener;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.tree.TreeSelectionModel;
public class File_Encryptor extends JFrame {
private JFrame thisFrame = this;
private JTree tree;
private JMenuBar jMenuBar1 = new JMenuBar();
private JMenuItem menuOpen = new JMenuItem("Open");
private JMenuItem menuSave = new JMenuItem("Save");
private JMenuItem menuClose = new JMenuItem("Close");
private JMenuItem menuQuit = new JMenuItem("Quit");
private JMenuItem menuAbout = new JMenuItem("About this software...");
private JMenuItem menuAdd = new JMenuItem("Add key and user");
private JMenuItem menuChange = new JMenuItem("Change buddy key");
private JMenuItem menuSend = new JMenuItem("Send your buddy key");
private JMenuItem menuDelete = new JMenuItem("Delete selected buddy key");
private JMenuItem menuReset = new JMenuItem("Reset your key");
private JMenuItem menuChangeLogin = new JMenuItem("Change Login");
private JMenuItem menuHelp = new JMenuItem("Help...");
private JButton openDir = new JButton("Open path");
private JTextField jTextField1 = new JTextField();
private JScrollPane treeView;
private JScrollPane imageView;
private JScrollPane textView;
private String ROOT;
private File root;
private DefaultMutableTreeNode top;
final private DefaultMutableTreeNode FILLER = new DefaultMutableTreeNode(new FileInfo ("about:blank", "about:blank"));
public File_Encryptor() throws FileNotFoundException, InterruptedException, IOException, ClassNotFoundException {
super("FILE ENCRYPTOR 1.0");
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
ROOT = getRoot(System.getProperty("user.home"));
root = new File(ROOT);
try{
//Create the nodes.
top = unfold(root);
top.setUserObject(new FileInfo(ROOT,ROOT));
tree = new JTree(top);
tree.getSelectionModel().setSelectionMode
(TreeSelectionModel.SINGLE_TREE_SELECTION);
Object nodage = top.getNextNode().getUserObject();
FileInfo leaf = (FileInfo) nodage;
tree.addTreeSelectionListener(new TreeSelectionListener() {
public void valueChanged(TreeSelectionEvent e) {
DefaultMutableTreeNode node = (DefaultMutableTreeNode)
tree.getLastSelectedPathComponent();
if (node == null) return;
try{
Object nodeInfo = node.getUserObject();
FileInfo temp = (FileInfo) nodeInfo;
if((node.isLeaf()) && (!(node.isRoot())))
System.out.println(temp.Path());
//figure out how to place file in editor pane.
else
return;
catch(Exception fubar)
fubar.printStackTrace();
treeView = new JScrollPane(tree);
treeView.setSize(150,450);
jTextField1.setMaximumSize(new Dimension(50, 100));
jTextField1.setText("PATH");
this.getContentPane().add(jTextField1, BorderLayout.EAST);
this.getContentPane().add(treeView, BorderLayout.WEST);
catch(Exception e) {
e.printStackTrace();
jMenuBar1.setBorder(BorderFactory.createEtchedBorder());
JMenu menu = new JMenu("File");
JMenu about = new JMenu("Help");
JMenu keys = new JMenu("Keys");
JMenu change = new JMenu("Login");
menuQuit.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_Q, ActionEvent.META_MASK));
menuQuit.setEnabled(true);
menuQuit.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.exit(0);
menu.add(menuQuit);
jMenuBar1.add(menu);
jMenuBar1.add(keys);
jMenuBar1.add(change);
jMenuBar1.add(about);
this.setJMenuBar(jMenuBar1);
public class FileInfo {
private String path = "";
private String name = "";
public FileInfo(String p , String n){
path = p;
name = n;
public String toString(){
return name;
public String Path(){
return path;
public static String getFileEx(String po){
String ext = "";
int i = po.lastIndexOf('.');
if(i > 0)
ext = po.substring(i-1);
else
ext = null;
return ext;
private DefaultMutableTreeNode unfold(File path) {
DefaultMutableTreeNode node = new DefaultMutableTreeNode("");
Vector Files = new Vector();
Vector Direc = new Vector();
if((path.isDirectory()) && (path.list().length != 0))
node = new DefaultMutableTreeNode(new FileInfo(path.getPath(),path.getName()));
File [] childs = path.listFiles();
for(int j = 0; j < childs.length; j++)
if(childs[j].isDirectory())
Direc.addElement(childs[j]);
else
Files.addElement(childs[j]);
for(int g = 0; g < Files.size(); g++)
Direc.addElement((File)Files.elementAt(g));
for(int i = 0; i < Direc.size(); i++)
node.add(unfold((File)Direc.elementAt(i)));
else if(!(path.isDirectory()))
node = new DefaultMutableTreeNode(new FileInfo(path.getPath(),path.getName()));
else
node = new DefaultMutableTreeNode(new FileInfo(path.getPath(),path.getName()));
node.add(new DefaultMutableTreeNode(new FileInfo(null,"<EMPTY FOLDER>")));
return node;
public static String getRoot(String path)
int find = path.indexOf(System.getProperty("file.separator"));
String root = path.substring(0,find + 1);
return root;
public static void main( String [ ] args )throws FileNotFoundException, InterruptedException, IOException, ClassNotFoundException {
File_Encryptor show = new File_Encryptor();
show.setSize(700, 500);
show.setResizable(false);
//show.setLocation(100,100);
show.setVisible(true);
//code end.
//well there it is. Hope someone can help me with my problem.
//I know this code is ugly, but I was trying a bunch of different
//things hoping something would work. but ehh no such luck.
//I am running windows 98, yea that's prolly my problem.
//thank you for your time.

Answer 1

I ran this on XP and got the null pointer exception...
it's likely that it's running into a file or directory that it can't list (in my case it was a mount on a different directory ntfs is kinda cool)... SO... to handle that problem I just put the whole method in a try / catch block
it was just the method unfold ... the fix returns a blank treenode... it should probably return null and the caller should see that as a sign to not add it to the tree...
     private DefaultMutableTreeNode unfold(File path) {
          DefaultMutableTreeNode node = new DefaultMutableTreeNode("");
          try
               Vector Files = new Vector();
               Vector Direc = new Vector();
               if(path==null)
                    return(node);
               if((path.isDirectory()) && (path.list().length != 0))
               node = new DefaultMutableTreeNode(new FileInfo(path.getPath(),path.getName()));
               File [] childs = path.listFiles();
               for(int j = 0; j < childs.length; j++)
               if(childs[j].isDirectory())
               Direc.addElement(childs[j]);
               else
               Files.addElement(childs[j]);
               for(int g = 0; g < Files.size(); g++)
               Direc.addElement((File)Files.elementAt(g));
               for(int i = 0; i < Direc.size(); i++)
               node.add(unfold((File)Direc.elementAt(i)));
               else if(!(path.isDirectory()))
               node = new DefaultMutableTreeNode(new FileInfo(path.getPath(),path.getName()));
               else
               node = new DefaultMutableTreeNode(new FileInfo(path.getPath(),path.getName()));
               node.add(new DefaultMutableTreeNode(new FileInfo(null,"<EMPTY FOLDER>")));
          catch (Exception e)
          return node;
     }