if (this.autoSort) {
            int index = Collections.binarySearch(this.data, item);
            if (index < 0) {
                this.data.add(-index - 1, item);
            }
            else {
                if (this.allowDuplicateXValues) {
                    // need to make sure we are adding *after* any duplicates
                    int size = this.data.size();
                    while (index < size 
                           && item.compareTo(this.data.get(index)) == 0) {
                        index++;
                    }
                    if (index < this.data.size()) {
                        this.data.add(index, item);
                    }
                    else {
                        this.data.add(item);
                    }
                }
                else {
                    throw new SeriesException("X-value already exists.");
                }
            }
        }
        else {
            if (!this.allowDuplicateXValues) {
                // can't allow duplicate values, so we need to check whether
                // there is an item with the given x-value already
                int index = indexOf(item.getX());
                if (index >= 0) {
                    throw new SeriesException("X-value already exists.");      
                }
            }
            this.data.add(item);
        }
        if (getItemCount() > this.maximumItemCount) {
            this.data.remove(0);
        }                    
        if (notify) {
            fireSeriesChanged();
        }
    }

    /**
     * Deletes a range of items from the series and sends a 
     * {@link SeriesChangeEvent} to all registered listeners.
     *
     * @param start  the start index (zero-based).
     * @param end  the end index (zero-based).
     */
    public void delete(int start, int end) {
        for (int i = start; i <= end; i++) {
            this.data.remove(start);
        }
        fireSeriesChanged();
    }

    /**
     * Removes the item at the specified index and sends a 
     * {@link SeriesChangeEvent} to all registered listeners.
     * 
     * @param index  the index.
     * 
     * @return The item removed.
     */
    public XYDataItem remove(int index) {
        XYDataItem result = (XYDataItem) this.data.remove(index);
        fireSeriesChanged();
        return result;
    }
    
    /**
     * Removes the item with the specified x-value and sends a 
     * {@link SeriesChangeEvent} to all registered listeners.
     * 
     * @param x  the x-value.

     * @return The item removed.
     */
    public XYDataItem remove(Number x) {
        return remove(indexOf(x));
    }
    
    /**
     * Removes all data items from the series.
     */
    public void clear() {
        if (this.data.size() > 0) {
            this.data.clear();
            fireSeriesChanged();
        }
    }

    /**
     * Return the data item with the specified index.
     *
     * @param index  the index.
     *
     * @return The data item with the specified index.
     */
    public XYDataItem getDataItem(int index) {
        return (XYDataItem) this.data.get(index);
    }

    /**
     * Returns the x-value at the specified index.
     *
     * @param index  the index (zero-based).
     *
     * @return The x-value (never <code>null</code>).
     */
    public Number getX(int index) {
        return getDataItem(index).getX();
    }

    /**
     * Returns the y-value at the specified index.
     *
     * @param index  the index (zero-based).
     *
     * @return The y-value (possibly <code>null</code>).
     */
    public Number getY(int index) {
        return getDataItem(index).getY();
    }
    
    /**
     * Updates the value of an item in the series and sends a 
     * {@link SeriesChangeEvent} to all registered listeners.
     *
     * @param index  the item (zero based index).
     * @param y  the new value (<code>null</code> permitted).
     * 
     * @deprecated Renamed updateByIndex(int, Number) to avoid confusion with
     *             the update(Number, Number) method.
     */
    public void update(int index, Number y) {
        XYDataItem item = getDataItem(index);
        item.setY(y);
        fireSeriesChanged();
    }
    
    /**
     * Updates the value of an item in the series and sends a 
     * {@link SeriesChangeEvent} to all registered listeners.
     * 
     * @param index  the item (zero based index).
     * @param y  the new value (<code>null</code> permitted).
     * 
     * @since 1.0.1
     */
    public void updateByIndex(int index, Number y) {
        update(index, y);
    }
    
    /**
     * Updates an item in the series.
     * 
     * @param x  the x-value (<code>null</code> not permitted).
     * @param y  the y-value (<code>null</code> permitted).
     * 
     * @throws SeriesException if there is no existing item with the specified
     *         x-value.
     */
    public void update(Number x, Number y) {
        int index = indexOf(x);
        if (index < 0) {
            throw new SeriesException("No observation for x = " + x);
        }
        else {
            XYDataItem item = getDataItem(index);
            item.setY(y);
            fireSeriesChanged();
        }
    }
    
    /**
     * Adds or updates an item in the series and sends a 
     * {@link org.jfree.data.general.SeriesChangeEvent} to all registered 
     * listeners.
     *
     * @param x  the x-value (<code>null</code> not permitted).
     * @param y  the y-value (<code>null</code> permitted).
     *
     * @return A copy of the overwritten data item, or <code>null</code> if no 
     *         item was overwritten.
     */
    public XYDataItem addOrUpdate(Number x, Number y) {
        if (x == null) {
            throw new IllegalArgumentException("Null 'x' argument.");   
        }
        XYDataItem overwritten = null;
        int index = indexOf(x);
        if (index >= 0) {
            XYDataItem existing = (XYDataItem) this.data.get(index);
            try {
                overwritten = (XYDataItem) existing.clone();
            }
            catch (CloneNotSupportedException e) {
                throw new SeriesException("Couldn't clone XYDataItem!");   
            }
            existing.setY(y);
        }
        else {
            // if the series is sorted, the negative index is a result from
            // Collections.binarySearch() and tells us where to insert the
            // new item...otherwise it will be just -1 and we should just
            // append the value to the list...
            if (this.autoSort) {
                this.data.add(-index - 1, new XYDataItem(x, y));
            }
            else {
                this.data.add(new XYDataItem(x, y));
            }
            // check if this addition will exceed the maximum item count...
            if (getItemCount() > this.maximumItemCount) {
                this.data.remove(0);
            }
        }            
        fireSeriesChanged();
        return overwritten;
    }

    /**
     * Returns the index of the item with the specified x-value, or a negative 
     * index if the series does not contain an item with that x-value.  Be 
     * aware that for an unsorted series, the index is found by iterating 
     * through all items in the series.
     * 
     * @param x  the x-value (<code>null</code> not permitted).
     * 
     * @return The index.
     */
    public int indexOf(Number x) {
        if (this.autoSort) {
            return Collections.binarySearch(this.data, new XYDataItem(x, null));   
        }
        else {
            for (int i = 0; i < this.data.size(); i++) {
                XYDataItem item = (XYDataItem) this.data.get(i);
                if (item.getX().equals(x)) {
                    return i;   
                }
            }
            return -1;
        }
    } 
    
    /**
     * Returns a clone of the series.
     *
     * @return A clone of the time series.
     * 
     * @throws CloneNotSupportedException if there is a cloning problem.
     */
    public Object clone() throws CloneNotSupportedException {
        Object clone = createCopy(0, getItemCount() - 1);
        return clone;
    }

    /**
     * Creates a new series by copying a subset of the data in this time series.
     *
     * @param start  the index of the first item to copy.
     * @param end  the index of the last item to copy.
     *
     * @return A series containing a copy of this series from start until end.
     * 
     * @throws CloneNotSupportedException if there is a cloning problem.
     */
    public XYSeries createCopy(int start, int end) 
        throws CloneNotSupportedException {

        XYSeries copy = (XYSeries) super.clone();
        copy.data = new java.util.ArrayList();
        if (this.data.size() > 0) {
            for (int index = start; index <= end; index++) {
                XYDataItem item = (XYDataItem) this.data.get(index);
                XYDataItem clone = (XYDataItem) item.clone();
                try {
                    copy.add(clone);
                }
                catch (SeriesException e) {
                    System.err.println("Unable to add cloned data item.");
                }
            }
        }
        return copy;

    }

    /**
     * Tests this series for equality with an arbitrary object.
     *
     * @param obj  the object to test against for equality 
     *             (<code>null</code> permitted).
     *
     * @return A boolean.
     */
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof XYSeries)) {
            return false;
        }
        if (!super.equals(obj)) {
            return false;
        }
        XYSeries that = (XYSeries) obj;
        if (this.maximumItemCount != that.maximumItemCount) {
            return false;
        }
        if (this.autoSort != that.autoSort) {
            return false;
        }
        if (this.allowDuplicateXValues != that.allowDuplicateXValues) {
            return false;
        }
        if (!ObjectUtilities.equal(this.data, that.data)) {
            return false;
        }
        return true;
    }
    
    /**
     * Returns a hash code.
     * 
     * @return A hash code.
     */
    public int hashCode() {
        int result = super.hashCode();
        result = 29 * result + (this.data != null ? this.data.hashCode() : 0);
        result = 29 * result + this.maximumItemCount;
        result = 29 * result + (this.autoSort ? 1 : 0);
        result = 29 * result + (this.allowDuplicateXValues ? 1 : 0);
        return result;
    }

}