public Dimension getPreferredSize() {
        int x = 0, y = 0;
        for (Iterator<ZElement> e = enumElements(); e.hasNext();) {
            MPDEntite o = (MPDEntite) e.next();
            x = o.getX() + o.getWidth() > x ? o.getX() + o.getWidth() : x;
            y = o.getY() + o.getHeight() > y ? o.getY() + o.getHeight() : y;
        }
        return new Dimension(x + 30, y + 30);
    }