Swing/HeaderColumnBackground のバックアップ(No.2)

class MonthTable extends JTable {
  @Override public void updateUI() {
    super.updateUI();
    JTableHeader header = getTableHeader();
    header.setResizingAllowed(false);
    header.setReorderingAllowed(false);
    updateWeekHeaderRenderer();
  }

  @Override protected JTableHeader createDefaultTableHeader() {
    return new JTableHeader(columnModel) {
      @Override public Dimension getPreferredSize() {
        Dimension d = super.getPreferredSize();
        JTable tbl = getTable();
        int rowCount = tbl.getModel().getRowCount() + 1;
        Class<JViewport> clz = JViewport.class;
        d.height = Optional.ofNullable(SwingUtilities.getAncestorOfClass(clz, tbl))
            .filter(clz::isInstance).map(clz::cast)
            .map(JViewport::getExtentSize)
            .map(dim -> dim.height / rowCount).orElse(24);
        return d;
      }
    };
  }

  @Override public void setModel(TableModel dataModel) {
    super.setModel(dataModel);
    EventQueue.invokeLater(this::updateWeekHeaderRenderer);
  }

  private void updateWeekHeaderRenderer() {
    TableColumnModel cm = getColumnModel();
    TableCellRenderer r = new WeekHeaderRenderer();
    for (int i = 0; i < cm.getColumnCount(); i++) {
      cm.getColumn(i).setHeaderRenderer(r);
    }
    getTableHeader().repaint();
  }
// ...
}

class WeekHeaderRenderer extends DefaultTableCellRenderer {
  public static final Color SUNDAY_BGC = new Color(0xB0_12_1A);
  public static final Color SATURDAY_BGC = new Color(0x1A_12_B0);
  private final WeekFields weekFields = WeekFields.of(Locale.getDefault());

  @Override public Component getTableCellRendererComponent(
        JTable table, Object value, boolean isSelected, boolean hasFocus,
        int row, int column) {
    Component c = super.getTableCellRendererComponent(
        table, value, isSelected, hasFocus, row, column);
    DayOfWeek week = weekFields.getFirstDayOfWeek().plus(column);
    if (week.equals(DayOfWeek.SUNDAY)) {
      c.setForeground(table.getSelectionForeground());
      c.setBackground(SUNDAY_BGC);
    } else if (week.equals(DayOfWeek.SATURDAY)) {
      c.setForeground(table.getSelectionForeground());
      c.setBackground(SATURDAY_BGC);
    } else {
      c.setForeground(table.getForeground());
      c.setBackground(table.getTableHeader().getBackground());
    }
    if (c instanceof JLabel) {
      JLabel l = (JLabel) c;
      l.setHorizontalAlignment(CENTER);
      Color gridColor = UIManager.getColor("Table.gridColor");
      Border border = BorderFactory.createMatteBorder(0, 0, 1, 1, gridColor);
      Border b = BorderFactory.createCompoundBorder(border, l.getBorder());
      l.setBorder(b);
    }
    return c;
  }
}