code: public String join(String separator) throws JSONException {
          JSONStringer stringer = new JSONStringer();
          stringer.open(JSONStringer.Scope.NULL, "");
          for (int i = 0, size = values.size(); i < size; i++) {
              if (i > 0) {
                  stringer.out.append(separator);
              }
              stringer.value(values.get(i));
          }
          stringer.close(JSONStringer.Scope.NULL, JSONStringer.Scope.NULL, "");
          return stringer.out.toString();
      }
docs: Returns a new string by alternating this array's values with {@code
  separator}. This array's string values are quoted and have their special
  characters escaped. For example, the array containing the strings '12"
  pizza', 'taco' and 'soda' joined on '+' returns this:
  <pre>"12\" pizza"+"taco"+"soda"</pre>