private transient Stroke domainGridlineStroke;

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

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

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

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