boolean isBST(Node root) { if (root == null) { return true; } return (isBST(root.left) && (isBST(root.right) && (root.left == null || root.left.data root.data)); }

binary tree is either empty (null reference), or is made of a single node, where the left and right pointers each point to a binary tree. suppose 'BinaryTree' is the name of the class representing the binary tree implementation. public static boolean isBinaryTree(Object obj){ if(!obj instanceof BinaryTree) return false; if(null == obj || null == obj.leftChild || obj == this.rightChild ) return true; else return obj.leftChild.isBinaryTree() && obj.rightChild.isBinaryTree(); }