code: public String mkString(NumberFormat formatter, String delimiter) {
          StringBuilder sb = new StringBuilder();
          VectorIterator it = iterator();
  
          while (it.hasNext()) {
              double x = it.next();
              int i = it.index();
              sb.append(formatter.format(x))
                      .append((i < length - 1 ? delimiter : ""));
          }
  
          return sb.toString();
      }
docs: Converts this vector into the string representation.
  
  @param formatter the number formatter
  @param delimiter the element's delimiter
  
  @return the vector converted to a string