Java JTree expand tree node by tree path

import java.util.Enumeration;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreeNode;
import javax.swing.tree.TreePath;
import javax.swing.tree.TreeSelectionModel;

public class Main {
   public static void main(String[] args) {
      DefaultMutableTreeNode rootNode = new DefaultMutableTreeNode("Root");
      DefaultMutableTreeNode a = new DefaultMutableTreeNode("A");
      rootNode.add(a);/*from w  w  w.  jav a  2  s . c  o  m*/

      DefaultMutableTreeNode a1 = new DefaultMutableTreeNode("1");
      a.add(a1);
      DefaultMutableTreeNode a2 = new DefaultMutableTreeNode("2");
      a.add(a2);

      DefaultMutableTreeNode b = new DefaultMutableTreeNode("B");
      rootNode.add(b);
      DefaultMutableTreeNode b1 = new DefaultMutableTreeNode("1");
      b.add(b1);

      JTree tree = new JTree(rootNode);
      
      expandAll(tree, new TreePath(rootNode), true);
      
      tree.getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);

      JFrame f = new JFrame();
      f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      f.add(new JScrollPane(tree));
      f.setSize(250, 250);
      f.setVisible(true);
   }
   private static void expandAll(JTree tree, TreePath parent, boolean expand) {
      TreeNode node = (TreeNode) parent.getLastPathComponent();
      if (node.getChildCount() >= 0) {
        for (Enumeration e = node.children(); e.hasMoreElements();) {
          TreeNode n = (TreeNode) e.nextElement();
          TreePath path = parent.pathByAddingChild(n);
          expandAll(tree, path, expand);
        }
      }
      if (expand) {
        tree.expandPath(parent);
      } else {
        tree.collapsePath(parent);
      }
    }
}