code: private static boolean isAsciiAlphaNum(String string) {
          for (int i = 0; i < string.length(); i++) {
              final char character = string.charAt(i);
              if (!(character >= 'a' && character <= 'z' ||
                      character >= 'A' && character <= 'Z' ||
                      character >= '0' && character <= '9')) {
                  return false;
              }
          }
  
          return true;
      }
docs: /*
  Checks whether a given string is an ASCII alphanumeric string.