public PathBetweenNodesEnumeration(TreeNode ancestor,
    TreeNode descendant) 
{
            super();
            if (ancestor == null || descendant == null) {
                throw new IllegalArgumentException("argument is null");
            }
            TreeNode current;
            stack = new Stack< TreeNode >();
            stack.push(descendant);
            current = descendant;
            while (current != ancestor) {
                current = current.getParent();
                if (current == null && descendant != ancestor) {
                    throw new IllegalArgumentException("node " + ancestor +
                                " is not an ancestor of " + descendant);
                }
                stack.push(current);
            }
}

 public boolean hasMoreElements() 
{
            return stack.size()  > 0;
}

 public TreeNode nextElement() 
{
            try {
                return stack.pop();
            } catch (EmptyStackException e) {
                throw new NoSuchElementException("No more elements");
            }
}