[LeetCode] Sum Root to Leaf Numbers

public class Solution {
    public int sumNumbers(TreeNode root) {
        int sum=0;
        TreeNode nowNode = root;
        Stack<TreeNode> nodeStack = new Stack<TreeNode>();
        boolean popNode = false;
        
        while (!(nowNode==root && popNode)) {
            if (!popNode) {
                if (nowNode != null) {
                    nodeStack.push(nowNode);
                    nowNode = nowNode.left;
                } else {
                    popNode = true;
                }
            } else {
                TreeNode topNode = nodeStack.peek();
                if (nowNode == topNode.right) {
                    if (topNode.left==null && topNode.right==null) {
                        sum = sum + getNumber(nodeStack);
                    }
                    nowNode = nodeStack.pop();
                } else {
                    nowNode = topNode.right;
                    popNode = false;
                }
            }
        }
        return sum;
    }
    
    public int getNumber(Stack<TreeNode> nodeStack) {
        int num = 0;
        for (Iterator<TreeNode> itor=nodeStack.iterator(); itor.hasNext();) {
            num = num*10 + itor.next().val;
        }
        
        return num;
    }
}