public PreorderEnumeration(TreeNode rootNode) 
{
            super();
            Vector v = new Vector(1);
            v.addElement(rootNode);     // PENDING: don't really need a vector
            stack = new Stack();
            stack.push(v.elements());
}

 public boolean hasMoreElements() 
{
            return (!stack.empty() &&
                    ((Enumeration)stack.peek()).hasMoreElements());
}

 public TreeNode nextElement() 
{
            Enumeration enumer = (Enumeration)stack.peek();
            TreeNode    node = (TreeNode)enumer.nextElement();
            Enumeration children = node.children();
            if (!enumer.hasMoreElements()) {
                stack.pop();
            }
            if (children.hasMoreElements()) {
                stack.push(children);
            }
            return node;
}