private void paintCellRelation(Graphics2D g) {
        Stroke originalStroke = g.getStroke();

        g.setStroke(new BasicStroke(STROKE_WIDTH));

        for (Cell cell : cells) {
            for (Arrow arrow : cell.getToArrowList()) {
                if (!arrows.contains(arrow)) {
                    arrows.add(arrow);
                }
                g.fill(arrow.getArrowArea());
            }
        }
        g.setStroke(originalStroke);
    }