public class XIntervalSeries extends ComparableObjectSeries {

    /**
     * Creates a new empty series.  By default, items added to the series will
     * be sorted into ascending order by x-value, and duplicate x-values will
     * be allowed (these defaults can be modified with another constructor.
     *
     * @param key  the series key (<code>null</code> not permitted).
     */
    public XIntervalSeries(Comparable key) {
        this(key, true, true);
    }

    /**
     * Constructs a new xy-series that contains no data.  You can specify
     * whether or not duplicate x-values are allowed for the series.
     *
     * @param key  the series key (<code>null</code> not permitted).
     * @param autoSort  a flag that controls whether or not the items in the
     *                  series are sorted.
     * @param allowDuplicateXValues  a flag that controls whether duplicate
     *                               x-values are allowed.
     */
    public XIntervalSeries(Comparable key, boolean autoSort,
            boolean allowDuplicateXValues) {
        super(key, autoSort, allowDuplicateXValues);
    }

    /**
     * Adds a data item to the series.
     *
     * @param x  the x-value.
     * @param y  the y-value.
     * @param xLow  the lower bound of the y-interval.
     * @param xHigh  the upper bound of the y-interval.
     */
    public void add(double x, double xLow, double xHigh, double y) {
        super.add(new XIntervalDataItem(x, xLow, xHigh, y), true);
    }

    /**
     * Returns the x-value for the specified item.
     *
     * @param index  the item index.
     *
     * @return The x-value (never <code>null</code>).
     */
    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();
    }

    /**
     * Returns the data item at the specified index.
     *
     * @param index  the item index.
     *
     * @return The data item.
     */
    public ComparableObjectItem getDataItem(int index) {
        return super.getDataItem(index);