throw new IllegalArgumentException("Null 'bar' argument.");
        }
        this.legendBar = bar;
        notifyListeners(new RendererChangeEvent(this));
    }
    
    /**
     * Initialises the renderer and returns a state object that should be 
     * passed to all subsequent calls to the drawItem() method.  Here we 
     * calculate the Java2D y-coordinate for zero, since all the bars have 
     * their bases fixed at zero.
     *
     * @param g2  the graphics device.
     * @param dataArea  the area inside the axes.
     * @param plot  the plot.
     * @param dataset  the data.
     * @param info  an optional info collection object to return data back to 
     *              the caller.
     *
     * @return A state object.
     */
    public XYItemRendererState initialise(Graphics2D g2,
                                          Rectangle2D dataArea,
                                          XYPlot plot,
                                          XYDataset dataset,
                                          PlotRenderingInfo info) {

        XYBarRendererState state = new XYBarRendererState(info);
        ValueAxis rangeAxis 
            = plot.getRangeAxisForDataset(plot.indexOf(dataset));
        state.setG2Base(
            rangeAxis.valueToJava2D(
                this.base, dataArea, plot.getRangeAxisEdge()
            )
        );
        return state;

    }

    /**
     * Returns a default legend item for the specified series.  Subclasses 
     * should override this method to generate customised items.
     *
     * @param datasetIndex  the dataset index (zero-based).
     * @param series  the series index (zero-based).
     *
     * @return A legend item for the series.
     */
    public LegendItem getLegendItem(int datasetIndex, int series) {
        LegendItem result = null;
        XYPlot xyplot = getPlot();
        if (xyplot != null) {
            XYDataset dataset = xyplot.getDataset(datasetIndex);
            if (dataset != null) {
                XYSeriesLabelGenerator lg = getLegendItemLabelGenerator();
                String label = lg.generateLabel(dataset, series);
                String description = label;
                String toolTipText = null;
                if (getLegendItemToolTipGenerator() != null) {
                    toolTipText = getLegendItemToolTipGenerator().generateLabel(
                        dataset, series
                    );
                }
                String urlText = null;
                if (getLegendItemURLGenerator() != null) {
                    urlText = getLegendItemURLGenerator().generateLabel(
                        dataset, series
                    );
                }
                Shape shape = this.legendBar;
                Paint paint = getSeriesPaint(series);
                Paint outlinePaint = getSeriesOutlinePaint(series);
                Stroke outlineStroke = getSeriesOutlineStroke(series);
                result = new LegendItem(label, description, toolTipText, 
                        urlText, shape, paint, outlineStroke, outlinePaint);
            }
        }
        return result;
    }
    
    /**
     * Draws the visual representation of a single data item.
     *
     * @param g2  the graphics device.
     * @param state  the renderer state.
     * @param dataArea  the area within which the plot is being drawn.
     * @param info  collects information about the drawing.
     * @param plot  the plot (can be used to obtain standard color 
     *              information etc).
     * @param domainAxis  the domain axis.
     * @param rangeAxis  the range axis.
     * @param dataset  the dataset.
     * @param series  the series index (zero-based).
     * @param item  the item index (zero-based).
     * @param crosshairState  crosshair information for the plot 
     *                        (<code>null</code> permitted).
     * @param pass  the pass index.
     */
    public void drawItem(Graphics2D g2,
                         XYItemRendererState state,
                         Rectangle2D dataArea,
                         PlotRenderingInfo info,
                         XYPlot plot,
                         ValueAxis domainAxis,
                         ValueAxis rangeAxis,
                         XYDataset dataset,
                         int series,
                         int item,
                         CrosshairState crosshairState,
                         int pass) {

        if (!getItemVisible(series, item)) {
            return;   
        }
        IntervalXYDataset intervalDataset = (IntervalXYDataset) dataset;

        double value0;
        double value1;
        if (this.useYInterval) {
            value0 = intervalDataset.getStartYValue(series, item);
            value1 = intervalDataset.getEndYValue(series, item);
        }
        else {
            value0 = this.base;
            value1 = intervalDataset.getYValue(series, item);
        }
        if (Double.isNaN(value0) || Double.isNaN(value1)) {
            return;
        }

        double translatedValue0 = rangeAxis.valueToJava2D(
            value0, dataArea, plot.getRangeAxisEdge()
        );
        double translatedValue1 = rangeAxis.valueToJava2D(
            value1, dataArea, plot.getRangeAxisEdge()
        );

        RectangleEdge location = plot.getDomainAxisEdge();
        Number startXNumber = intervalDataset.getStartX(series, item);
        if (startXNumber == null) {
            return;
        }
        double translatedStartX = domainAxis.valueToJava2D(
            startXNumber.doubleValue(), dataArea, location
        );

        Number endXNumber = intervalDataset.getEndX(series, item);
        if (endXNumber == null) {
            return;
        }
        double translatedEndX = domainAxis.valueToJava2D(
            endXNumber.doubleValue(), dataArea, location
        );

        double translatedWidth = Math.max(
            1, Math.abs(translatedEndX - translatedStartX)
        );
        double translatedHeight = Math.abs(translatedValue1 - translatedValue0);

        if (getMargin() > 0.0) {
            double cut = translatedWidth * getMargin();
            translatedWidth = translatedWidth - cut;
            translatedStartX = translatedStartX + cut / 2;
        }

        Rectangle2D bar = null;
        PlotOrientation orientation = plot.getOrientation();
        if (orientation == PlotOrientation.HORIZONTAL) {
            bar = new Rectangle2D.Double(
                Math.min(translatedValue0, translatedValue1), 
                Math.min(translatedStartX, translatedEndX),
                translatedHeight, translatedWidth);
        }
        else if (orientation == PlotOrientation.VERTICAL) {
            bar = new Rectangle2D.Double(
                Math.min(translatedStartX, translatedEndX), 
                Math.min(translatedValue0, translatedValue1), 
                translatedWidth, translatedHeight);
        }

        Paint itemPaint = getItemPaint(series, item);
        if (getGradientPaintTransformer() 
                != null && itemPaint instanceof GradientPaint) {
            GradientPaint gp = (GradientPaint) itemPaint;
            itemPaint = getGradientPaintTransformer().transform(gp, bar);
        }
        g2.setPaint(itemPaint);
        g2.fill(bar);
        if (isDrawBarOutline() 
                && Math.abs(translatedEndX - translatedStartX) > 3) {
            Stroke stroke = getItemOutlineStroke(series, item);
            Paint paint = getItemOutlinePaint(series, item);
            if (stroke != null && paint != null) {
                g2.setStroke(stroke);
                g2.setPaint(paint);
                g2.draw(bar);                
            }
        }
        
        // TODO: we need something better for the item labels
        if (isItemLabelVisible(series, item)) {
            drawItemLabel(
                g2, orientation, dataset, series, item, bar.getCenterX(), 
                bar.getY(), value1 < 0.0
            );
        }

        // add an entity for the item...
        if (info != null) {
            EntityCollection entities = info.getOwner().getEntityCollection();
            if (entities != null) {
                String tip = null;
                XYToolTipGenerator generator 
                    = getToolTipGenerator(series, item);
                if (generator != null) {
                    tip = generator.generateToolTip(dataset, series, item);
                }
                String url = null;
                if (getURLGenerator() != null) {
                    url = getURLGenerator().generateURL(dataset, series, item);
                }
                XYItemEntity entity = new XYItemEntity(
                    bar, dataset, series, item, tip, url
                );
                entities.add(entity);
            }
        }

    }

    /**
     * Returns the lower and upper bounds (range) of the x-values in the 
     * specified dataset.  Since this renderer uses the x-interval in the 
     * dataset, this is taken into account for the range.
     * 
     * @param dataset  the dataset (<code>null</code> permitted).
     * 
     * @return The range (<code>null</code> if the dataset is 
     *         <code>null</code> or empty).
     */
    public Range findDomainBounds(XYDataset dataset) {
        if (dataset != null) {
            return DatasetUtilities.findDomainBounds(dataset, true);
        }
        else {
            return null;
        }
    }

    /**
     * Returns a clone of the renderer.
     *
     * @return A clone.
     *
     * @throws CloneNotSupportedException  if the renderer cannot be cloned.
     */
    public Object clone() throws CloneNotSupportedException {
        XYBarRenderer result = (XYBarRenderer) super.clone();
        if (this.gradientPaintTransformer != null) {
            result.gradientPaintTransformer = (GradientPaintTransformer)
                ObjectUtilities.clone(this.gradientPaintTransformer);
        }
        return result;
    }

    /**
     * Tests this renderer for equality with an arbitrary object.
     * 
     * @param obj  the object to test against (<code>null</code> permitted).
     * 
     * @return A boolean.
     */
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof XYBarRenderer)) {
            return false;
        }
        if (!super.equals(obj)) {
            return false;
        }
        XYBarRenderer that = (XYBarRenderer) obj;
        if (this.base != that.base) {
            return false;
        }
        if (this.drawBarOutline != that.drawBarOutline) {
            return false;
        }
        if (this.margin != that.margin) {
            return false;
        }
        if (this.useYInterval != that.useYInterval) {
            return false;
        }
        if (!ObjectUtilities.equal(
            this.gradientPaintTransformer, that.gradientPaintTransformer)
        ) {
            return false;
        }
        if (!ShapeUtilities.equal(this.legendBar, that.legendBar)) {
            return false;   
        }
        return true;
    }
    
    /**
     * Provides serialization support.
     *
     * @param stream  the input stream.
     *
     * @throws IOException  if there is an I/O error.
     * @throws ClassNotFoundException  if there is a classpath problem.
     */
    private void readObject(ObjectInputStream stream) 
            throws IOException, ClassNotFoundException {
        stream.defaultReadObject();
        this.legendBar = SerialUtilities.readShape(stream);
    }
    
    /**
     * Provides serialization support.
     *
     * @param stream  the output stream.
     *
     * @throws IOException  if there is an I/O error.
     */
    private void writeObject(ObjectOutputStream stream) throws IOException {
        stream.defaultWriteObject();
        SerialUtilities.writeShape(this.legendBar, stream);
    }

}