Pontos no JFreeChart

public class GerandoGrafico extends ApplicationFrame {

    private Principal objeto = null;
    private ExpressaoMatematica func = null;

    public GerandoGrafico(Principal obj, String title) {

        super(title);

        objeto = obj;
        
        //System.out.println(objeto.funcao.getText());
        
        func = new ExpressaoMatematica(objeto.funcao.getText());

        JPanel chartPanel = createPanel();

        chartPanel.setPreferredSize(new java.awt.Dimension(500, 270));

        setContentPane(chartPanel);

//------------------------- TROCANDO O  ÍCONE DA JANELA ----------------------//
/*        BufferedImage image = null;
        File file = new File(C:\\icone.png);

        try {

            image = ImageIO.read(file);

        } catch (IOException e) {

            e.printStackTrace();

        }

        this.setIconImage(image);*/
//----------------------------------------------------------------------------//

    }

    private XYDataset createDataset() {

        double inicio = Double.valueOf(objeto.inicio_intervalo.getText());
        double fim = Double.valueOf(objeto.fim_intervalo.getText());

        //System.out.println(inicio);
        //System.out.println(fim);

        Function2D f1 = new Function2D() {

            public double getValue(double x) {

                //System.out.println(func.value(x));

                return(func.value(x));

            }

        };

        return(DatasetUtilities.sampleFunction2D(f1,inicio,fim, 100,f(x)));

    }

    private JFreeChart createChart(XYDataset dataset) {

        // create the chart...
        JFreeChart chart = ChartFactory.createXYLineChart(

                f(x) =  + objeto.funcao.getText(),    // chart title
                Eixo X,                      // x axis label
                Eixo Y,                      // y axis label
                dataset,                  // data
                PlotOrientation.VERTICAL,
                true,                     // include legend
                true,                     // tooltips
                false                     // urls

         );


        // NOW DO SOME OPTIONAL CUSTOMISATION OF THE CHART...
        chart.setBackgroundPaint(Color.white);

        // get a reference to the plot for further customisation...
        XYPlot plot = (XYPlot) chart.getPlot();
        plot.setBackgroundPaint(Color.lightGray);
        plot.setAxisOffset(new RectangleInsets(5.0, 5.0, 5.0, 5.0));
        plot.setDomainGridlinePaint(Color.white);
        plot.setRangeGridlinePaint(Color.white);

        XYLineAndShapeRenderer renderer = (XYLineAndShapeRenderer) plot.getRenderer();
        renderer.setShapesVisible(false);

        XYLineAndShapeRenderer renderer2 = new XYLineAndShapeRenderer(true, false);
        plot.setRenderer(1, renderer2);

        // change the auto tick unit selection to integer units only...
        NumberAxis rangeAxis = (NumberAxis) plot.getRangeAxis();
        rangeAxis.setStandardTickUnits(NumberAxis.createIntegerTickUnits());
        // OPTIONAL CUSTOMISATION COMPLETED.

        return(chart);

    }

    public JPanel createPanel() {

        JFreeChart chart = createChart(createDataset());
        
        return(new ChartPanel(chart));

   }

   public void iniciarGrafico() {

      GerandoGrafico demo = new GerandoGrafico(objeto, Gráfico da Função);

      demo.pack();

      //RefineryUtilities.centerFrameOnScreen(demo);

      demo.setLocation(0, 0);

      demo.setVisible(true);

   }

}