code: public TOTP build() {
          long time = System.currentTimeMillis();
          return new TOTP(generateTOTP(time), time, hmacShaAlgorithm, digits, timeStep);
      }
docs: Build a Time-based One-time Password {@link TOTP} using the current
  system time (current time in milliseconds since the UNIX epoch). Note
  that the builder instance can be reused for subsequent
  configuration/generation calls.
  
  @return a Time-based One-time Password {@link TOTP} instance.