mirror iter bt java

// http://code2begin.blogspot.com
// program to create mirror of a given binary tree recursively

/**
 * Created by MOHIT on 25-05-2018.
 */
import java.util.*;
import static java.lang.Integer.max;

// node class
class node{
    int data;
    node left;
    node right;

    // function that returns a pointer to new node
    public node(int element){
        this.data = element;
        this.left = null;
        this.right = null;

    }
};


public class BinaryTree {

    // function to convert tree into mirror tree iteratively
    static void mirror_tree(node root){
        // if the node is null then return
        if (root == null){
        return;
        }

        // creating a stack to keep the child pointers
        Stack STACK = new Stack<node>();

        // push root node on the stack
        STACK.push(root);

        while (!STACK.isEmpty()){

            // remove the top node from the stack
            node current = (node)STACK.peek();
            STACK.pop();

            // swap the left and right nodes
            node temp = current.left;
            current.left = current.right;
            current.right = temp;

            // as it is a stack, we push right child node first because we want to access it after operating on the left child
            if (current.right != null){
                STACK.push(current.right);
            }
            if (current.left != null){
                STACK.push(current.left);
            }
        }
    }

    // function to print the preorder traversal of a binary tree
    public static void preorder(node root) {
        if (root == null) {
            return;
        }
        System.out.print(root.data + " ");
        preorder(root.left);
        preorder(root.right);
    }


    public static void main(String arg[]) {
        node m1 = new node(8);
        m1.left = new node(3);
        m1.right = new node(10);
        m1.left.left = new node(1);
        m1.left.right = new node(6);
        m1.left.right.left = new node(4);
        m1.left.right.right = new node(7);
        m1.right.right = new node(14);
        m1.right.right.left = new node(13);

        node m2 = new node(8);
        m2.right = new node(3);
        m2.left = new node(10);
        m2.left.left = new node(14);
        m2.right.left = new node(6);
        m2.right.right = new node(1);
        m2.left.left.right = new node(13);
        m2.right.left.left = new node(7);
        m2.right.left.right = new node(4);

        System.out.println("Tree #1 before mirroring : ");
        preorder(m1);
        System.out.println("\nTree #1 after mirroring : ");
        mirror_tree(m1);
        preorder(m1);
        System.out.println("\n\nTree #2 is mirror of Tree #1 to check the correctness : ");
        System.out.println("TREE #1 : ");
        preorder(m1);
        System.out.println("\nTREE #2 : ");
        preorder(m2);

    }
}