code: private void nextMonthActionPerformed (ActionEvent evt)
      {
          calendar.setTime(targetPanelDate);
          calendar.add(Calendar.MONTH, 1);
          calendar.set(Calendar.HOUR_OF_DAY, 12);
          calendar.set(Calendar.MINUTE, 0);
          calendar.set(Calendar.SECOND, 0);
          calendar.set(Calendar.MILLISECOND, 0);
          targetPanelDate = calendar.getTime();
          this.layoutCalendar(targetPanelDate);
      }
docs: User pressed the "next month" button, change the calendar.
  @param evt The action event (ignored).