JTableの水平罫線を描画する位置とその色をソート条件に応じて変更する

class BorderPaintLayerUI extends LayerUI<JScrollPane> {
  @Override public void paint(Graphics g, JComponent c) {
    super.paint(g, c);
    JTable table = getTable(c);
    RowSorter<? extends TableModel> sorter = table == null ? null : table.getRowSorter();
    if (Objects.nonNull(sorter)) {
      List<? extends RowSorter.SortKey> keys = sorter.getSortKeys();
      int column = keys.isEmpty() ? -1 : keys.get(0).getColumn();
      if (column <= 0 || column == 9) {
        Graphics2D g2 = (Graphics2D) g.create();
        boolean b1 = column == 0 && keys.get(0).getSortOrder() == SortOrder.ASCENDING;
        boolean b2 = column == 9 && keys.get(0).getSortOrder() == SortOrder.DESCENDING;
        if (column < 0 || b1 || b2) {
          g2.setPaint(Color.GREEN.darker());
          g2.draw(makeUnderline(c, table, 2));
          g2.setPaint(Color.BLUE.darker());
          g2.draw(makeUnderline(c, table, 6));
          g2.setPaint(Color.RED.darker());
          g2.draw(makeUnderline(c, table, 20));
        } else {
          g2.setPaint(Color.GREEN.darker());
          g2.draw(makeUnderline(c, table, 22 - 2));
          g2.setPaint(Color.BLUE.darker());
          g2.draw(makeUnderline(c, table, 22 - 6));
          g2.setPaint(Color.RED.darker());
          g2.draw(makeUnderline(c, table, 22 - 20));
        }
        g2.dispose();
      }
    }
  }

  private static JTable getTable(Component c) {
    JTable table = null;
    if (c instanceof JLayer) {
      Component c1 = ((JLayer<?>) c).getView();
      if (c1 instanceof JScrollPane) {
        table = (JTable) ((JScrollPane) c1).getViewport().getView();
      }
    }
    return table;
  }

  private static Line2D makeUnderline(JComponent c, JTable table, int idx) {
    Rectangle r0 = table.getCellRect(idx - 1, 0, false);
    Rectangle r1 = table.getCellRect(idx - 1, table.getColumnCount() - 1, false);
    Rectangle r = SwingUtilities.convertRectangle(table, r0.union(r1), c);
    return new Line2D.Double(r.getX(), r.getMaxY(), r.getMaxX(), r.getMaxY());
  }
}