public String getToolTipText(int series, int item) {

        String result = null;

        if (series < getListCount()) {
            List tooltips = (List) this.toolTipSeries.get(series);
            if (tooltips != null) {
                if (item < tooltips.size()) {
                    result = (String) tooltips.get(item);
                }
            }
        }

        return result;