code: private char stringChar() throws JsonParserException {
      int c = advanceChar();
      if (c == -1)
        throw createParseException(null, "String was not terminated before end of input", true);
      if (c < 32)
        throw createParseException(null,
            "Strings may not contain control characters: 0x" + Integer.toString(c, 16), false);
      return (char)c;
    }
docs: Advances a character, throwing if it is illegal in the context of a JSON string.