series.addChangeListener(this);
        fireDatasetChanged();
    }

    /**
     * Removes the specified series from the collection and sends a 
     * {@link DatasetChangeEvent} to all registered listeners.
     *
     * @param series  the series (<code>null</code> not permitted).
     */
    public void removeSeries(TimeSeries series) {
        if (series == null) {
            throw new IllegalArgumentException("Null 'series' argument.");
        }
        this.data.remove(series);
        series.removeChangeListener(this);
        fireDatasetChanged();
    }

    /**
     * Removes a series from the collection.
     *
     * @param index  the series index (zero-based).
     */
    public void removeSeries(int index) {
        TimeSeries series = getSeries(index);
        if (series != null) {
            removeSeries(series);
        }
    }

    /**
     * Removes all the series from the collection and sends a 
     * {@link DatasetChangeEvent} to all registered listeners.
     */
    public void removeAllSeries() {

        // deregister the collection as a change listener to each series in the
        // collection
        for (int i = 0; i < this.data.size(); i++) {
            TimeSeries series = (TimeSeries) this.data.get(i);
            series.removeChangeListener(this);
        }

        // remove all the series from the collection and notify listeners.
        this.data.clear();
        fireDatasetChanged();

    }

    /**
     * Returns the number of items in the specified series.  This method is 
     * provided for convenience.
     *
     * @param series  the series index (zero-based).
     *
     * @return The item count.
     */
    public int getItemCount(int series) {
        return getSeries(series).getItemCount();
    }
    
    /**
     * Returns the x-value (as a double primitive) for an item within a series.
     * 
     * @param series  the series (zero-based index).
     * @param item  the item (zero-based index).
     * 
     * @return The x-value.
     */
    public double getXValue(int series, int item) {
        TimeSeries s = (TimeSeries) this.data.get(series);
        TimeSeriesDataItem i = s.getDataItem(item);
        RegularTimePeriod period = i.getPeriod();
        return getX(period);
    }

    /**
     * Returns the x-value for the specified series and item.
     *
     * @param series  the series (zero-based index).
     * @param item  the item (zero-based index).
     *
     * @return The value.
     */
    public Number getX(int series, int item) {
        TimeSeries ts = (TimeSeries) this.data.get(series);
        TimeSeriesDataItem dp = ts.getDataItem(item);
        RegularTimePeriod period = dp.getPeriod();
        return new Long(getX(period));
    }
    
    /**
     * Returns the x-value for a time period.
     *
     * @param period  the time period.
     *
     * @return The x-value.
     */
    protected synchronized long getX(RegularTimePeriod period) {
        long result = 0L;
        if (this.xPosition == TimePeriodAnchor.START) {
            result = period.getFirstMillisecond(this.workingCalendar);
        }
        else if (this.xPosition == TimePeriodAnchor.MIDDLE) {
            result = period.getMiddleMillisecond(this.workingCalendar);
        }
        else if (this.xPosition == TimePeriodAnchor.END) {
            result = period.getLastMillisecond(this.workingCalendar); 
        }
        return result;
    }

    /**
     * Returns the starting X value for the specified series and item.
     *
     * @param series  the series (zero-based index).
     * @param item  the item (zero-based index).
     *
     * @return The value.
     */
    public synchronized Number getStartX(int series, int item) {
        TimeSeries ts = (TimeSeries) this.data.get(series);
        TimeSeriesDataItem dp = ts.getDataItem(item);
        return new Long(dp.getPeriod().getFirstMillisecond(
                this.workingCalendar));
    }

    /**
     * Returns the ending X value for the specified series and item.
     *
     * @param series The series (zero-based index).
     * @param item  The item (zero-based index).
     *
     * @return The value.
     */
    public synchronized Number getEndX(int series, int item) {
        TimeSeries ts = (TimeSeries) this.data.get(series);
        TimeSeriesDataItem dp = ts.getDataItem(item);
        return new Long(dp.getPeriod().getLastMillisecond(
                this.workingCalendar));
    }

    /**
     * Returns the y-value for the specified series and item.
     *
     * @param series  the series (zero-based index).
     * @param item  the item (zero-based index).
     *
     * @return The value (possibly <code>null</code>).
     */
    public Number getY(int series, int item) {
        TimeSeries ts = (TimeSeries) this.data.get(series);
        TimeSeriesDataItem dp = ts.getDataItem(item);
        return dp.getValue();
    }

    /**
     * Returns the starting Y value for the specified series and item.
     *
     * @param series  the series (zero-based index).
     * @param item  the item (zero-based index).
     *
     * @return The value (possibly <code>null</code>).
     */
    public Number getStartY(int series, int item) {
        return getY(series, item);
    }

    /**
     * Returns the ending Y value for the specified series and item.
     *
     * @param series  te series (zero-based index).
     * @param item  the item (zero-based index).
     *
     * @return The value (possibly <code>null</code>).
     */
    public Number getEndY(int series, int item) {
        return getY(series, item);
    }


    /**
     * Returns the indices of the two data items surrounding a particular 
     * millisecond value.  
     * 
     * @param series  the series index.
     * @param milliseconds  the time.
     * 
     * @return An array containing the (two) indices of the items surrounding 
     *         the time.
     */
    public int[] getSurroundingItems(int series, long milliseconds) {
        int[] result = new int[] {-1, -1};
        TimeSeries timeSeries = getSeries(series);
        for (int i = 0; i < timeSeries.getItemCount(); i++) {
            Number x = getX(series, i);
            long m = x.longValue();
            if (m <= milliseconds) {
                result[0] = i;
            }
            if (m >= milliseconds) {
                result[1] = i;
                break;
            }
        }
        return result;
    }
    
    /**
     * Returns the minimum x-value in the dataset.
     *
     * @param includeInterval  a flag that determines whether or not the
     *                         x-interval is taken into account.
     * 
     * @return The minimum value.
     */
    public double getDomainLowerBound(boolean includeInterval) {
        double result = Double.NaN;
        Range r = getDomainBounds(includeInterval);
        if (r != null) {
            result = r.getLowerBound();
        }
        return result;        
    }

    /**
     * Returns the maximum x-value in the dataset.
     *
     * @param includeInterval  a flag that determines whether or not the
     *                         x-interval is taken into account.
     * 
     * @return The maximum value.
     */
    public double getDomainUpperBound(boolean includeInterval) {
        double result = Double.NaN;
        Range r = getDomainBounds(includeInterval);
        if (r != null) {
            result = r.getUpperBound();
        }
        return result;
    }

    /**
     * Returns the range of the values in this dataset's domain.
     *
     * @param includeInterval  a flag that determines whether or not the
     *                         x-interval is taken into account.
     * 
     * @return The range.
     */
    public Range getDomainBounds(boolean includeInterval) {
        Range result = null;
        Iterator iterator = this.data.iterator();
        while (iterator.hasNext()) {
            TimeSeries series = (TimeSeries) iterator.next();
            int count = series.getItemCount();
            if (count > 0) {
                RegularTimePeriod start = series.getTimePeriod(0);
                RegularTimePeriod end = series.getTimePeriod(count - 1);
                Range temp;
                if (!includeInterval) {
                    temp = new Range(getX(start), getX(end));
                }
                else {
                    temp = new Range(
                            start.getFirstMillisecond(this.workingCalendar),
                            end.getLastMillisecond(this.workingCalendar));
                }
                result = Range.combine(result, temp);
            }
        }
        return result;
    }
    
    /**
     * Tests this time series collection for equality with another object.
     *
     * @param obj  the other object.
     *
     * @return A boolean.
     */
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof TimeSeriesCollection)) {
            return false;
        }
        TimeSeriesCollection that = (TimeSeriesCollection) obj;
        if (this.xPosition != that.xPosition) {
            return false;
        }
        if (this.domainIsPointsInTime != that.domainIsPointsInTime) {
            return false;
        }
        if (!ObjectUtilities.equal(this.data, that.data)) {
            return false;
        }
        return true;
    }

    /**
     * Returns a hash code value for the object.
     *
     * @return The hashcode
     */
    public int hashCode() {
        int result;
        result = this.data.hashCode();
        result = 29 * result + (this.workingCalendar != null 
                ? this.workingCalendar.hashCode() : 0);
        result = 29 * result + (this.xPosition != null 
                ? this.xPosition.hashCode() : 0);
        result = 29 * result + (this.domainIsPointsInTime ? 1 : 0);
        return result;
    }
    
}