code: public String toSentenceString(ArrayList s) {
      StringBuilder sb = new StringBuilder();
      for (int wordNum = start(), end = end(); wordNum <= end; wordNum++) {
        sb.append(s.get(wordNum));
        if (wordNum != end) {
          sb.append(" ");
        }
      }
      return sb.toString();
    }
docs: TODO: genericize this!