Expanding path on JTree

Question

Hi.
I add a node to the default tree model and an event gets fired back to the listener (in this case the JTree itself). I then expand the path so as to show the new node to the user. A gap appears between the new node and the node in another branch below the new node. If I force a re-render (like with updateUI - erk!) the tree is drawn fine, otherwise its now. See the diagram below. If this a common problem and how do you fix it? Many thanks!
A +
|
+----B
|
+----C
Now I insert a node D, and I get:
A +
|
+----B
| |
| +----D
| <------- big gap :-(
|
+----C                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   

Answer 1

import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.tree.*;
public class Test extends JFrame {
  JTree jt = new JTree();
  JButton jb = new JButton("Add");
  public Test() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    Container content = getContentPane();
    content.add(new JScrollPane(jt),BorderLayout.CENTER);
    jt.setExpandsSelectedPaths(true);
    JButton jb = new JButton("Add");
    content.add(jb, BorderLayout.SOUTH);
    jb.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ae) {
        TreePath tp = jt.getSelectionPath();
        if (tp!=null) {
          DefaultMutableTreeNode dmtn = (DefaultMutableTreeNode)tp.getLastPathComponent();
          DefaultMutableTreeNode newDmtn = new DefaultMutableTreeNode("Something");
          dmtn.add(newDmtn);
          ((javax.swing.tree.DefaultTreeModel)jt.getModel()).nodeStructureChanged(dmtn);
          jt.setSelectionPath(new TreePath(newDmtn.getPath()));
    setSize(200, 300);
    show();
  public static void main(String args[]) { new Test(); }
}