code: private void setSizeOfMonthYearPanel() {
          // Skip this function if the settings have not been applied.
          if (settings == null) {
              return;
          }
          // Get the font metrics object.
          Font font = labelMonth.getFont();
          Canvas canvas = new Canvas();
          FontMetrics metrics = canvas.getFontMetrics(font);
          // Calculate the preferred height for the month and year panel.
          int heightNavigationButtons = buttonPreviousYear.getPreferredSize().height;
          int preferredHeightMonthLabel = labelMonth.getPreferredSize().height;
          int preferredHeightYearLabel = labelYear.getPreferredSize().height;
          int monthFontHeight = metrics.getHeight();
          int monthFontHeightWithPadding = monthFontHeight + 2;
          int panelHeight = Math.max(monthFontHeightWithPadding, Math.max(preferredHeightMonthLabel,
              Math.max(preferredHeightYearLabel, heightNavigationButtons)));
          // Get the length of the longest translated month string (in pixels).
          DateFormatSymbols symbols = DateFormatSymbols.getInstance(settings.getLocale());
          String[] allLocalMonths = symbols.getMonths();
          int longestMonthPixels = 0;
          for (String month : allLocalMonths) {
              int monthPixels = metrics.stringWidth(month);
              longestMonthPixels = (monthPixels > longestMonthPixels) ? monthPixels : longestMonthPixels;
          }
          int yearPixels = metrics.stringWidth("_2000");
          // Calculate the size of a box to hold the text with some padding.
          Dimension size = new Dimension(longestMonthPixels + yearPixels + 12, panelHeight);
          // Set the monthAndYearPanel to the appropriate constant size.
          monthAndYearOuterPanel.setMinimumSize(size);
          monthAndYearOuterPanel.setPreferredSize(size);
          // monthAndYearOuterPanel.setMaximumSize(size);
          // Redraw the panel.
          this.doLayout();
          this.validate();
      }
docs: setSizeOfMonthYearPanel, This sets the size of the panel at the top of the calendar that
  holds the month and the year label. The size is calculated from the largest month name (in
  pixels), that exists in locale and language that is being used by the date picker.