code: public static String join(CharSequence delimiter, Iterable tokens) {
          StringBuilder sb = new StringBuilder();
          boolean firstTime = true;
          for (Object token: tokens) {
              if (firstTime) {
                  firstTime = false;
              } else {
                  sb.append(delimiter);
              }
              sb.append(token);
          }
          return sb.toString();
      }
docs: Returns a string containing the tokens joined by delimiters.
  @param tokens an array objects to be joined. Strings will be formed from
  the objects by calling object.toString().