public Number getX(int index) {
        XIntervalDataItem item = (XIntervalDataItem) getDataItem(index);
        return item.getX();
    }

    /**
     * Returns the lower bound of the x-interval for the specified item.
     *
     * @param index  the item index.
     *
     * @return The lower bound of the x-interval.
     *
     * @since 1.0.10
     */
    public double getXLowValue(int index) {
        XIntervalDataItem item = (XIntervalDataItem) getDataItem(index);
        return item.getXLowValue();
    }

    /**
     * Returns the upper bound of the x-interval for the specified item.
     *
     * @param index  the item index.
     *
     * @return The upper bound of the x-interval.
     *
     * @since 1.0.10
     */
    public double getXHighValue(int index) {
        XIntervalDataItem item = (XIntervalDataItem) getDataItem(index);
        return item.getXHighValue();
    }

    /**
     * Returns the y-value for the specified item.
     *
     * @param index  the item index.
     *
     * @return The y-value.
     */
    public double getYValue(int index) {
        XIntervalDataItem item = (XIntervalDataItem) getDataItem(index);
        return item.getYValue();