check BST java

// http://code2begin.blogspot.com
// program to check if a given binary tree is a Binary search tree or not

/**
 * Created by MOHIT on 25-05-2018.
 */

import java.io.*;
import java.lang.reflect.Array;
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 check if the given binary tree is a BST or not
    static boolean check_BST(node current){
        if(current == null){
            return true;
        }

        if (current.left != null && current.data < current.left.data){
            return false;
        }
        if (current.right != null && current.data > current.right.data){
            return false;
        }
        return (check_BST(current.left) && check_BST(current.right));
    }


    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);

        node head2 = new node(5);
        head2.left = new node(2);
        head2.right = new node(12);
        head2.left.left = new node(-4);
        head2.left.right = new node(3);
        head2.right.left = new node(9);
        head2.right.right = new node(21);
        head2.right.right.left = new node(19);
        head2.right.right.right = new node(25);

        node head3 = new node(1);
        head3.left = new node(2);
        head3.right = new node(3);
        head3.left.left = new node(4);
        head3.left.right = new node(5);
        head3.right.right = new node(6);
        head3.left.left.right = new node(7);
        head3.right.right.left = new node(8);
        head3.left.left.right.left = new node(9);
        head3.left.left.right.left.left = new node(10);
        head3.right.right.left.right = new node(11);

        System.out.println("Binary Tree #1 is a Binary Search Tree : " + check_BST(head));
        System.out.println("Binary Tree #2 is a Binary Search Tree : " + check_BST(head2));
        System.out.println("Binary Tree #3 is a Binary Search Tree : " + check_BST(head3));
    }
}