CSC301: Tree code: Non-nullable [48/56]

    public int size () {
        if (root == null) return 0;
        return size (root);
    }
    private static int size (Node x) {
        int sz = 1;
        if (x.left != null) sz += size (x.left);
        if (x.right != null) sz += size (x.right);
        return sz;
    }

In this code, we check for null, then make the call.

The variable x is non-nullable (must not be assigned null)

Lets call this the non-nullable version.

We might also call this cautious, or Look before you leap!