Iterative PostOrder Traversal

    public static <E> void nonRecursive(BTNode<E> root)
    {
        Stack<BTNode<E>> S = new Stack<BTNode<E>>();
        while (1 != 0)
        {
            if (root != null)
            {
                S.push(root);
                root = root.getLeft();
            }
            else
            {
                if (S.isEmpty())
                {
                    break;
                }
                else if (S.peek().getRight() == null)
                {
                    root = S.pop();
                    System.out.print(root.getData() + " ");
                    if (root == S.peek().getRight())
                    {
                        System.out.print(S.peek().getData() + " ");
                        S.pop();
                    }
                }
                if (!S.isEmpty())
                {
                    root = S.peek().getRight();
                }
                else
                    root = null;
            }
        }
    }