CSC403: Printing: Print prefix [2/10]

    public void printPre () {
        printPre (root);
        StdOut.println ();
    }
    private static void printPre (Node x) {
        if (x == null) return;
        StdOut.print (x.key + " ");
        printPre (x.left);
        printPre (x.right);
    }

Print prefix (simple version).

What about infix? postfix?