Java Program to Perform Postorder Non-Recursive Traversal of a Given Binary Tree

This is a java program to construct a binary tree and perform postorder traversal of the constructed binary tree.
Nodes visited are in the order:
visit Left node
visit Right node
visit Root node

Here is the source code of the Java Program to Perform Postorder Non-Recursive Traversal of a Given Binary Tree. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

//This is a java program to implement non recursive post order traversal of Binary Search Tree
import java.util.Scanner;
import java.util.Stack;
 
class BinarySearchTreeNode
{
    BinarySearchTreeNode left, right;
    int                  data;
 
    public BinarySearchTreeNode()
    {
        left = null;
        right = null;
        data = 0;
    }
 
    public BinarySearchTreeNode(int n)
    {
        left = null;
        right = null;
        data = n;
    }
 
    public void setLeft(BinarySearchTreeNode n)
    {
        left = n;
    }
 
    public void setRight(BinarySearchTreeNode n)
    {
        right = n;
    }
 
    public BinarySearchTreeNode getLeft()
    {
        return left;
    }
 
    public BinarySearchTreeNode getRight()
    {
        return right;
    }
 
    public void setData(int d)
    {
        data = d;
    }
 
    public int getData()
    {
        return data;
    }
}
 
class BinarySearchTreeOperations
{
    private BinarySearchTreeNodes root;
 
    public BinarySearchTreeOperations()
    {
        root = null;
    }
 
    public boolean isEmpty()
    {
        return root == null;
    }
 
    public void insert(int data)
    {
        root = insert(root, data);
    }
 
    private BinarySearchTreeNodes insert(BinarySearchTreeNodes node, int data)
    {
        if (node == null)
            node = new BinarySearchTreeNodes(data);
        else
        {
            if (data <= node.getData())
                node.left = insert(node.left, data);
            else
                node.right = insert(node.right, data);
        }
        return node;
    }
 
    public void postorder()
    {
        postorder(root);
    }
 
    private void postorder(BinarySearchTreeNodes r)
    {
        if (root == null)
            return;
 
        final Stack<BinarySearchTreeNodes> stack = new Stack<BinarySearchTreeNodes>();
        BinarySearchTreeNodes node = root;
 
        while (!stack.isEmpty() || node != null)
        {
            while (node != null)
            {
                if (node.right != null)
                    stack.add(node.right);
                stack.add(node);
                node = node.left;
            }
 
            node = stack.pop();
 
            if (node.right != null && !stack.isEmpty()
                    && node.right == stack.peek())
            {
                BinarySearchTreeNodes nodeRight = stack.pop();
                stack.push(node);
                node = nodeRight;
            } else
            {
                System.out.print(node.data + " ");
                node = null;
            }
        }
    }
}
 
public class Postorder_NonRecursive_BST
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        BinarySearchTreeOperations bst = new BinarySearchTreeOperations();
        System.out.println("Enter the first 10 elements of the tree\n");
        int N = 10;
        for (int i = 0; i < N; i++)
            bst.insert(scan.nextInt());
 
        System.out.print("\nPost order : ");
        bst.postorder();
 
        scan.close();
    }
}

Output:

$ javac Postorder_NonRecursive_BST.java
$ java Postorder_NonRecursive_BST
 
Enter the first 10 elements of the tree
 
12 4 10 13 15 46 78 98 45 12
 
Post order : 12 10 4 45 98 78 46 15 13 12