Java JTree get children node for a node

import java.awt.Container;
import java.awt.FlowLayout;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;

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

public class Main {
   public static void main(String args[]) {
      final JFrame f = new JFrame("JTree Demo");
      f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      Container c = f.getContentPane();
      c.setLayout(new FlowLayout());
      DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");
      DefaultMutableTreeNode c1 = new DefaultMutableTreeNode("X");
      DefaultMutableTreeNode c2 = new DefaultMutableTreeNode("B");
      DefaultMutableTreeNode c3 = new DefaultMutableTreeNode("C");
      root.add(c1);/*from  ww w  . java  2s  .c o  m*/
      root.add(c2);
      root.add(c3);

      c1.add(new DefaultMutableTreeNode("1"));
      c1.add(new DefaultMutableTreeNode("2"));

      c2.add(new DefaultMutableTreeNode("3"));
      c2.add(new DefaultMutableTreeNode("4"));

      c3.add(new DefaultMutableTreeNode("5"));
      DefaultMutableTreeNode n6 = new DefaultMutableTreeNode("6");
      n6.setUserObject("demo2s.com");
      c3.add(n6);

      JTree t = new JTree(root);

      List<DefaultMutableTreeNode> list = getDefaultMutableTreeNodeChildren(root);
      System.out.println(list);

      c.add(new JScrollPane(t));
      f.pack();
      f.setVisible(true);
   }

   public static List<DefaultMutableTreeNode> getDefaultMutableTreeNodeChildren(
         TreeNode node) {
     if (node == null) {
         throw new NullPointerException("node == null");
     }
     List<DefaultMutableTreeNode> children = new ArrayList<>(
             node.getChildCount());
     for (Enumeration<?> enumeration = node.children(); enumeration
             .hasMoreElements();) {
         Object nextElement = enumeration.nextElement();

         if (nextElement instanceof DefaultMutableTreeNode) {
             children.add((DefaultMutableTreeNode) nextElement);
         }
     }
     return children;
 }
}