Java DefaultMutableTreeNode create

import java.awt.Container;
import java.awt.FlowLayout;

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

public class Main {
   public static void main(String args[]) {
      final JFrame f = new JFrame("JTree Demo");
      Container c = f.getContentPane();
      c.setLayout(new FlowLayout());
      DefaultMutableTreeNode root = new DefaultMutableTreeNode("Computer"); 
      DefaultMutableTreeNode c1 = new DefaultMutableTreeNode("A");
      DefaultMutableTreeNode c2 = new DefaultMutableTreeNode("B");
      DefaultMutableTreeNode c3 = new DefaultMutableTreeNode("C");
      root.add(c1);/*from w w  w .  j  a  v a  2 s.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"));
      c3.add(new DefaultMutableTreeNode("6"));

      JTree t = new JTree(root);
      c.add(t);
      f.pack();
      f.setVisible(true);
   }
}