How to calculate the depth of a binary search tree

Question

I would like to calculate the summation of the depths of each node of a Binary Search Tree.

The individual depths of the elements are not already stored.

Answer 1

private static int getNumberOfNodes(Node node) {
    if (node == null) {
        return 0;
    }

    return 1 + getNumberOfNodes(node.left) + getNumberOfNodes(node.right);
}