This demo is intended to show the right way to interact with the nodes in a DefaultTreeModel .

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JFrame;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JPopupMenu;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.SwingUtilities;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.TreePath;
import javax.swing.tree.TreeSelectionModel;

/**
 * DefaultTreeModelDemoPanel This class is intended to demonstrate the right and
 * wrong ways to manipulate a DefaultTreeModel.
 * 
 * @author Collin Fagan
 */
public class DefaultTreeModelDemoPanel extends JPanel {

   private DefaultMutableTreeNode rootNode = new DefaultMutableTreeNode("Root");

   private DefaultMutableTreeNode child1Node = new DefaultMutableTreeNode(
         "Child 1");

   private DefaultMutableTreeNode child2Node = new DefaultMutableTreeNode(
         "Child 2");

   private DefaultMutableTreeNode child3Node = new DefaultMutableTreeNode(
         "Child 3");

   private JTree tree = new JTree(rootNode);

   private JPopupMenu menu = new JPopupMenu("Operations");

   /**
    * 
    */
   public DefaultTreeModelDemoPanel() {
      setLayout(new BorderLayout());
      add(new JScrollPane(tree));
      tree.getSelectionModel().setSelectionMode(
            TreeSelectionModel.SINGLE_TREE_SELECTION);
      tree.setShowsRootHandles(true);
      tree.addMouseListener(treeMenuClicked);

      rootNode.add(child1Node);
      rootNode.add(child2Node);
      rootNode.add(child3Node);

      JMenuItem removeNode = new JMenuItem(
            "Remove from node - [Will NOT update correctly]");
      removeNode.setToolTipText("Will NOT update correctly");
      removeNode.addActionListener(removeNodeFromNode);

      JMenuItem removeModel = new JMenuItem("Remove from model");
      removeModel.setToolTipText("Will update correctly");
      removeModel.addActionListener(removeNodeFromModel);

      JMenuItem addNumbers = new JMenuItem("Add 50 children");
      addNumbers.setToolTipText("Example of a bulk update");
      addNumbers.addActionListener(addEvenOddNumbers);

      JMenuItem longTextNoUpdate = new JMenuItem(
            "Set long text - without update - [Will NOT update correctly]");
      longTextNoUpdate.setToolTipText("Will NOT update correctly");
      longTextNoUpdate.addActionListener(modifyUserObjectWithoutUpdate);

      JMenuItem longTextWithManUpdate = new JMenuItem(
            "Set long text - with manual update");
      longTextWithManUpdate.setToolTipText("Will update correctly");
      longTextWithManUpdate.addActionListener(modifyUserObjectWithManualUpdate);
      
      JMenuItem longTextWithAutoUpdate = new JMenuItem(
      "Set long text - with automatic update");
      longTextWithAutoUpdate.setToolTipText("Will update correctly");
      longTextWithAutoUpdate.addActionListener(modifyUserObjectWithAutomaticUpdate);

      menu.add(removeNode);
      menu.add(removeModel);
      menu.addSeparator();
      menu.add(addNumbers);
      menu.addSeparator();
      menu.add(longTextNoUpdate);
      menu.add(longTextWithManUpdate);
      menu.add(longTextWithAutoUpdate);
   }

   /**
    * MouseAdapter to popup the menu the tree menu
    */
   private MouseAdapter treeMenuClicked = new MouseAdapter() {

      public void mousePressed(MouseEvent e) {
         maybeShowPopup(e);
      }

      public void mouseReleased(MouseEvent e) {
         maybeShowPopup(e);
      }

      private void maybeShowPopup(MouseEvent e) {
         if (e.isPopupTrigger()) {
            int row = tree.getClosestRowForLocation(e.getX(), e.getY());
            tree.setSelectionPath(tree.getPathForRow(row));
            menu.show(tree, e.getX(), e.getY());
         }
      }
   };

   /**
    * Example of the WRONG way to remove a single node from a tree. This will
    * not update the tree correctly.
    */
   private ActionListener removeNodeFromNode = new ActionListener() {

      /**
       * @see java.awt.event.ActionListener#actionPerformed(java.awt.event.ActionEvent)
       */
      public void actionPerformed(ActionEvent e) {
         TreePath currentSelection = tree.getSelectionPath();
         if (currentSelection != null) {
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) currentSelection
                  .getLastPathComponent();

            node.removeFromParent();
         }
      }
   };

   /**
    * Example of the CORRECT way to remove a single node from a tree.
    */
   private ActionListener removeNodeFromModel = new ActionListener() {

      /**
       * @see java.awt.event.ActionListener#actionPerformed(java.awt.event.ActionEvent)
       */
      public void actionPerformed(ActionEvent e) {

         TreePath currentSelection = tree.getSelectionPath();
         if (currentSelection != null) {
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) currentSelection
                  .getLastPathComponent();
            DefaultTreeModel model = ((DefaultTreeModel) tree.getModel());
            model.removeNodeFromParent(node);
         }
      }
   };

   /**
    * Example of adding children in bulk, then updating the tree.
    */
   private ActionListener addEvenOddNumbers = new ActionListener() {

      /**
       * @see java.awt.event.ActionListener#actionPerformed(java.awt.event.ActionEvent)
       */
      public void actionPerformed(ActionEvent e) {

         TreePath currentSelection = tree.getSelectionPath();
         if (currentSelection != null) {
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) currentSelection
                  .getLastPathComponent();
            DefaultTreeModel model = ((DefaultTreeModel) tree.getModel());

            for (int i = 0; i < 50; i++) {
               node.add(new DefaultMutableTreeNode(i));
            }
            // The above changes may not seem to take effect until
            // nodeStructureChanged is called
            model.nodeStructureChanged(node);
         }
      }
   };

   /**
    * Example of the setting the user object and NOT updating the model. This
    * will NOT update the tree correctly.
    */
   private ActionListener modifyUserObjectWithoutUpdate = new ActionListener() {

      /**
       * @see java.awt.event.ActionListener#actionPerformed(java.awt.event.ActionEvent)
       */
      public void actionPerformed(ActionEvent e) {
         TreePath currentSelection = tree.getSelectionPath();
         if (currentSelection != null) {
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) currentSelection
                  .getLastPathComponent();

            node.setUserObject("THIS IS A VERY LOOOOOOOOOOOOOOOOOOOOONG STRING");
         }
      }
   };

   /**
    * Example of setting the user object and updating the model. This WILL
    * update the tree correctly.
    */
   private ActionListener modifyUserObjectWithManualUpdate = new ActionListener() {

      /**
       * @see java.awt.event.ActionListener#actionPerformed(java.awt.event.ActionEvent)
       */
      public void actionPerformed(ActionEvent e) {
         TreePath currentSelection = tree.getSelectionPath();
         if (currentSelection != null) {            
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) currentSelection
                  .getLastPathComponent();

            node.setUserObject("THIS IS A VERY LOOOOOOOOOOOOOOOOOOOOONG STRING");

            DefaultTreeModel model = ((DefaultTreeModel) tree.getModel());
            model.nodeChanged(node);
         }
      }
   };
   
   /**
    * Example of setting the user object and updating the model. This WILL
    * update the tree correctly.
    */
   private ActionListener modifyUserObjectWithAutomaticUpdate = new ActionListener() {

      /**
       * @see java.awt.event.ActionListener#actionPerformed(java.awt.event.ActionEvent)
       */
      public void actionPerformed(ActionEvent e) {
         TreePath currentSelection = tree.getSelectionPath();
         if (currentSelection != null) {
            DefaultTreeModel model = ((DefaultTreeModel) tree.getModel());
            model.valueForPathChanged(currentSelection, "THIS IS A VERY LOOOOOOOOOOOOOOOOOOOOONG STRING");
         }
      }
   };

   /**
    * Main program entry point, starts the demo.
    * 
    * @param args
    */
   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {

         public void run() {
            JFrame demoFrame = new JFrame("DefaultTreeModel Demo");
            demoFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
            demoFrame.setContentPane(new DefaultTreeModelDemoPanel());
            demoFrame.setSize(300, 600);
            // centers the frame on the screen
            demoFrame.setLocationRelativeTo(null);

            demoFrame.setVisible(true);
         }
      });
   }
}