JTableのセルBorderをホバー効果でハイライトする

private final class MonthTable extends JTable {
  private final Point pt = new Point(-1000, -1000);
  private transient MouseAdapter listener;

  @Override public void updateUI() {
    removeMouseListener(listener);
    removeMouseMotionListener(listener);
    super.updateUI();
    setFillsViewportHeight(true);
    setOpaque(false);
    setShowGrid(false);
    setIntercellSpacing(new Dimension(2, 2));
    setFont(getFont().deriveFont(Font.BOLD));
    setDefaultRenderer(LocalDate.class, new CalendarTableRenderer());
    JTableHeader header = getTableHeader();
    TableCellRenderer r = new CenterAlignmentHeaderRenderer();
    TableColumnModel cm = getColumnModel();
    EventQueue.invokeLater(() -> {
      for (int i = 0; i < cm.getColumnCount(); i++) {
        cm.getColumn(i).setHeaderRenderer(r);
      }
    });
    header.setResizingAllowed(false);
    header.setReorderingAllowed(false);
    listener = new SpotlightListener();
    addMouseListener(listener);
    addMouseMotionListener(listener);
  }

  @Override protected void paintComponent(Graphics g) {
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setRenderingHint(
        RenderingHints.KEY_ANTIALIASING,
        RenderingHints.VALUE_ANTIALIAS_ON);
    g2.setComposite(AlphaComposite.Src);
    Point2D center = new Point2D.Float(pt.x, pt.y);
    float[] dist = {0.0f, 0.5f, 1.0f};
    Color[] colors = {Color.GRAY, Color.LIGHT_GRAY, Color.WHITE};
    Rectangle cr = getCellRect(0, 0, true);
    int r = Math.max(cr.width, cr.height) * 2;
    g2.setPaint(new RadialGradientPaint(center, r, dist, colors));
    int r2 = r + r;
    g2.fill(new Ellipse2D.Float(pt.x - r, pt.y - r, r2, r2));
    g2.dispose();
    super.paintComponent(g);
  }

  private final class SpotlightListener extends MouseAdapter {
    @Override public void mouseExited(MouseEvent e) {
      pt.setLocation(-1000, -1000);
      repaint();
    }

    @Override public void mouseEntered(MouseEvent e) {
      update(e);
    }

    @Override public void mouseDragged(MouseEvent e) {
      update(e);
    }

    @Override public void mouseMoved(MouseEvent e) {
      update(e);
    }

    private void update(MouseEvent e) {
      pt.setLocation(e.getPoint());
      Rectangle cr = getCellRect(0, 0, true);
      int r = Math.max(cr.width, cr.height) * 2;
      int r2 = r + r;
      repaint(new Rectangle(pt.x - r, pt.y - r, r2, r2));
    }
  }

  // ...
}