mirror rec bt java

// 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 return mirror of the binary tree
    static void mirror_tree_recursive(node root){
        if (root == null){
            return;
        }else{
            // creating mirror using postorder traversal
            mirror_tree_recursive(root.left);
            mirror_tree_recursive(root.right);

            node temp = root.left;
            root.left = root.right;
            root.right = temp;
        }
    }
    // 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_recursive(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);

    }
}