public static void validateNotExists(File f) throws IOException {
    if (f.exists()) {
      throw new IOException(String.format("%s exists, please choose another file\n", f));
    }
  }
Validates whether {@code publicExponent} is odd and greater than 65536.

<p>The primes p and q are chosen such that (p-1)(q-1) is relatively prime to the public
exponent. Therefore, the public exponent must be odd. Furthermore, choosing a public exponent
which is not greater than 65536 can lead to weak instantiations of RSA. A public exponent which
is odd and greater than 65536 conforms to the requirements set by NIST FIPS 186-4
(Appendix B.3.1).

@throws GeneralSecurityException if {@code publicExponent} is even or not greater than 65536.
java_src/src/main/java/com/google/crypto/tink/subtle/Validators.java