boundary traversal java

// http://code2begin.blogspot.com
// program to print boundary traversal of a given binary tree

/**
 * Created by MOHIT on 25-05-2018.
 */
import java.util.*;

// 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 print the left boundary of the tree
    static void print_left_boundary(node root){
        if (root != null){
            if (root.left != null){
                System.out.print(root.data + " ");
                print_left_boundary(root.left);
            }else if (root.right != null){
                System.out.print(root.data + " ");
                print_left_boundary(root.right);
            }
        }
        return;
    }


    // function to print the left boundary of the tree
    static void print_right_boundary(node root){
        if (root != null){
            if (root.right != null){
                print_right_boundary(root.right);
                System.out.print(root.data + " ");
            }else if (root.left != null){
                print_right_boundary(root.left);
                System.out.print(root.data + " ");
            }
        }
        return;
    }

    // function to print the leaf nodes of the binary tree
    static void print_leaves(node root){
        if (root != null){
            print_leaves(root.left);
            if(root.left == null && root.right == null){
                System.out.print(root.data + " ");
            }
            print_leaves(root.right);
        }
    }

    // function to print the boundary traversal of the binary tree
    static void boundary_traversal(node root){
        print_left_boundary(root);
        print_leaves(root);
        print_right_boundary(root);
        return;
    }

    public static void main(String arg[]) {
        node head = new node(1);
        head.left = new node(2);
        head.right = new node(3);
        head.left.left = new node(4);
        head.left.right = new node(5);
        head.right.right = new node(6);
        head.left.left.right = new node(7);
        head.right.right.left = new node(8);
        head.left.left.right.left = new node(9);
        head.left.left.right.left.left = new node(10);
        head.right.right.left.right = new node(11);
        System.out.print("Boundary traversal of the binary tree is : ");
        boundary_traversal(head);
    }
}