Write a standalone recursive Java method, int countFull(TreeNode root) that, given a reference to the root node of a binary tree, returns the number of full nodes (ones that have two children) in that tree. Assume a standard Binary TreeNode implementation with left child and right child references.

Here is what I have for returning the total number of nodes in a tree:

int countNodes(TreeNode root) {

return root == null ? 0 : 1 + countNodes(root.left) + countNodes(root.right);

}