Determine weather a given Binary Tree is BST.java

class Node
{
    int data;
    Node left = null, right = null;
 
    Node(int data) {
        this.data = data;
    }
}
 
class Main
{
    public static Node insert(Node root, int key)
    {
        if (root == null) {
            return new Node(key);
        }
 
        if (key < root.data) {
            root.left = insert(root.left, key);
        }
        else {
            root.right = insert(root.right, key);
        }
 
        return root;
    }
 
    public static boolean isBST(Node node, int minKey, int maxKey)
    {
        if (node == null) {
            return true;
        }
 
        if (node.data < minKey || node.data > maxKey) {
            return false;
        }
 
        return isBST(node.left, minKey, node.data) &&
            isBST(node.right, node.data, maxKey);
    }
 
    public static void isBST(Node root)
    {
        if (isBST(root, Integer.MIN_VALUE, Integer.MAX_VALUE)) {
            System.out.println("The tree is a BST.");
        }
        else {
            System.out.println("The tree is not a BST!");
        }
    }
 
    private static void swap(Node root)
    {
        Node left = root.left;
        root.left = root.right;
        root.right = left;
    }
 
    public static void main(String[] args)
    {
        int[] keys = { 15, 10, 20, 8, 12, 16, 25 };
 
        Node root = null;
        for (int key: keys) {
            root = insert(root, key);
        }
 
        swap(root);
        isBST(root);
    }
}