code: public static String quote(char ch) {
          switch (ch) {
          case '\b':  return "\\b";
          case '\f':  return "\\f";
          case '\n':  return "\\n";
          case '\r':  return "\\r";
          case '\t':  return "\\t";
          case '\'':  return "\\'";
          case '\"':  return "\\\"";
          case '\\':  return "\\\\";
          default:
              return (isPrintableAscii(ch))
                  ? String.valueOf(ch)
                  : String.format("\\u%04x", (int) ch);
          }
      }
docs: Escapes a character if it has an escape sequence or is
  non-printable ASCII.  Leaves non-ASCII characters alone.