code: @Override
    public DurationFormatterFactory setPeriodFormatter(
        PeriodFormatter formatter) {
      if (formatter != this.formatter) {
        this.formatter = formatter;
        reset();
      }
      return this;
    }
docs: Set the period formatter used by the factory.  New formatters created
  with this factory will use the given period formatter.
  
  @return this BasicDurationFormatterFactory