code: public static String join(String _delimiter, List<String> _strings) {
          if (_strings == null) {
              return null;
          }
          if (_delimiter == null) {
              _delimiter = "";
          }
          StringBuilder sb = new StringBuilder();
          for (int i = 0; i < _strings.size(); i++) {
              sb.append(_strings.get(i));
              if (i < _strings.size() - 1) { // only append delimiter if this is not the last token
                  sb.append(_delimiter);
              }
          }
          return sb.toString();
      }
docs: Combines the Strings in _string using _delimiter.
  @param _delimiter delimiting string
  @param _strings strings to join
  @return null if _strings is null, concatenated string otherwise