java 实现动态改变树形结构中主节点的名称

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.*;
import javax.swing.event.TreeModelEvent;
import javax.swing.event.TreeModelListener;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.tree.*;
import javax.swing.border.TitledBorder;

import java.awt.event.InputEvent;
import java.awt.event.KeyEvent;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.awt.event.MouseListener;

public class sdf
{
String nodeName = null; //原有节点名称
DefaultMutableTreeNode root;
DefaultMutableTreeNode node1;
DefaultMutableTreeNode node2;
DefaultMutableTreeNode node3;
DefaultMutableTreeNode node4;

JTree tree;
DefaultTreeModel treeModel;
    DefaultMutableTreeNode leafnode;
frametest1 frame1; 

  public sdf()
  {   

JFrame frame=new JFrame("kekelian");
    frame.setIconImage(Toolkit.getDefaultToolkit().createImage("D:\\study\\主题.png"));
    Container contentPane=frame.getContentPane();     
    Container con=new Container();      
    JMenuBar menubar1 = new JMenuBar();     
frame.setJMenuBar(menubar1);
JMenu menu1 = new JMenu("File");
menu1.setMnemonic('F'); 
menubar1.add(menu1);

JMenuItem item1 = new JMenuItem("Open      ");
item1.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_O,
InputEvent.CTRL_MASK));
menu1.add(item1);

      
    root=new DefaultMutableTreeNode("Primary database");
    node1=new DefaultMutableTreeNode("Point");
    node2=new DefaultMutableTreeNode("Line");
    node3=new DefaultMutableTreeNode("Pane");
    node4=new DefaultMutableTreeNode("Volume");
    root.add(node1);