private transient Stroke domainGridlineStroke;

    /** The paint used to draw the domain  grid-lines. */
    private transient Paint domainGridlinePaint;

    /**
     * A flag that controls whether the grid-lines for the range axis are
     * visible.
     */
    private boolean rangeGridlinesVisible;

    /** The stroke used to draw the range axis grid-lines. */
    private transient Stroke rangeGridlineStroke;

    /** The paint used to draw the range axis grid-lines. */
    private transient Paint rangeGridlinePaint;