code: @Override
      protected int calculateTabWidth(final int tabPlacement, final int tabIndex, final FontMetrics metrics) {
          if (_pane.getSeparators().contains(tabIndex)) {
              return SEPARATOR_WIDTH;
          }
          int width = super.calculateTabWidth(tabPlacement, tabIndex, metrics);
          if (!_pane.getUnclosables().contains(tabIndex)) {
              width += CLOSE_ICON_WIDTH;
          }
          return width;
      }
docs: Override this to provide extra space on right for close button