code: public static String toLowerString(String s) {
          int len = s.length();
          int idx = 0;
          for (; idx < len; idx++) {
              if (isUpper(s.charAt(idx))) {
                  break;
              }
          }
          if (idx == len) {
              return s;
          }
  
          char[] buf = new char[len];
          for (int i = 0; i < len; i++) {
              char c = s.charAt(i);
              buf[i] = (i < idx) ? c : toLower(c);
          }
          return new String(buf);
      }
docs: Converts the given ASCII String to lower-case.