### Question:
XYDifferenceRenderer extends AbstractXYItemRenderer implements XYItemRenderer, PublicCloneable { @Override public LegendItem getLegendItem(int datasetIndex, int series) { LegendItem result = null; XYPlot p = getPlot(); if (p != null) { XYDataset dataset = p.getDataset(datasetIndex); if (dataset != null) { if (getItemVisible(series, 0)) { String label = getLegendItemLabelGenerator().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); } Paint paint = lookupSeriesPaint(series); Stroke stroke = lookupSeriesStroke(series); Shape line = getLegendLine(); result = new LegendItem(label, description, toolTipText, urlText, line, stroke, paint); result.setLabelFont(lookupLegendTextFont(series)); Paint labelPaint = lookupLegendTextPaint(series); if (labelPaint != null) { result.setLabelPaint(labelPaint); } result.setDataset(dataset); result.setDatasetIndex(datasetIndex); result.setSeriesKey(dataset.getSeriesKey(series)); result.setSeriesIndex(series); } } } return result; } XYDifferenceRenderer();  XYDifferenceRenderer(Paint positivePaint, Paint negativePaint,
                                boolean shapes); Paint getPositivePaint(); void setPositivePaint(Paint paint); Paint getNegativePaint(); void setNegativePaint(Paint paint); boolean getShapesVisible(); void setShapesVisible(boolean flag); Shape getLegendLine(); void setLegendLine(Shape line); boolean getRoundXCoordinates(); void setRoundXCoordinates(boolean round); @Override XYItemRendererState initialise(Graphics2D g2,
                                          Rectangle2D dataArea,
                                          XYPlot plot,
                                          XYDataset data,
                                          PlotRenderingInfo info); @Override int getPassCount(); @Override 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); @Override LegendItem getLegendItem(int datasetIndex, int series); @Override boolean equals(Object obj); @Override Object clone();  }### Answer:
@Test public void testGetLegendItemSeriesIndex() { XYSeriesCollection d1 = new XYSeriesCollection(); XYSeries s1 = new XYSeries("S1"); s1.add(1.0, 1.1); XYSeries s2 = new XYSeries("S2"); s2.add(1.0, 1.1); d1.addSeries(s1); d1.addSeries(s2); XYSeriesCollection d2 = new XYSeriesCollection(); XYSeries s3 = new XYSeries("S3"); s3.add(1.0, 1.1); XYSeries s4 = new XYSeries("S4"); s4.add(1.0, 1.1); XYSeries s5 = new XYSeries("S5"); s5.add(1.0, 1.1); d2.addSeries(s3); d2.addSeries(s4); d2.addSeries(s5); XYDifferenceRenderer r = new XYDifferenceRenderer(); XYPlot plot = new XYPlot(d1, new NumberAxis("x"), new NumberAxis("y"), r); plot.setDataset(1, d2); new JFreeChart(plot); LegendItem li = r.getLegendItem(1, 2); assertEquals("S5", li.getLabel()); assertEquals(1, li.getDatasetIndex()); assertEquals(2, li.getSeriesIndex()); }