Algoritm for Preorder Tree Traversals : Iterative Model(Non-Recursive way)

import java.util.Stack; //Preorder Tree Traversals : Iterative Model(Non-Recursive way) class BinaryTreePreOrderTraversalIterativeModel {      class TreeNode {             TreeNode left, right;             int data; // considering integer data.                    public TreeNode(int dataItem) {                   this.data = dataItem;                   left = null;                   right = null;             }      }              TreeNode root;        BinaryTreePreOrderTraversalIterativeModel() {              root = null;        }               void printPerOrderTraversal(TreeNode treeNode) {              if(treeNode == null)                     return;                           //Data, Left, Right                           Stack<TreeNode> s = new Stack<TreeNode>();              s.push(root);              while(!s.isEmpty()) {                     TreeNode currentNode = s.pop();                     System.out.println(currentNode.data);                                         if(currentNode.right != null) {                           s.push(currentNode.right);                     }                                         if(currentNode.left != null) {                           s.push(currentNode.left);                     }              }        }               void printPerOrder() {              printPerOrderTraversal(root);        }        public static void main(String[] args) {              BinaryTreePreOrderTraversalIterativeModel tree = new BinaryTreePreOrderTraversalIterativeModel();              tree.root = new TreeNode(1);                      tree.root.left = new TreeNode(2);              tree.root.right = new TreeNode(3);                      tree.root.left.left = new TreeNode(4);              tree.root.left.right = new TreeNode(5);                      tree.root.right.left = new TreeNode(6);              tree.root.right.right = new TreeNode(7);                      tree.printPerOrder();        } } //Time Complexity: O(n). Space Complexity: O(n).

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