Changing shape of single point in JFreeChart XYPLot

ChartFactory.createScatterPlot() instantiates an XYLineAndShapeRenderer. You can replace the renderer with one that lets you selectively replace the Shape returned by getItemShape(), as shown below.

    xyPlot.setRenderer(new XYLineAndShapeRenderer(false, true) {

        @Override
        public Shape getItemShape(int row, int col) {
            if (row == 0 & col == N) {
                return ShapeUtilities.createDiagonalCross(5, 2);
            } else {
                return super.getItemShape(row, col);
            }
        }
    });

Complete example, as run:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Shape;
import java.util.*;
import javax.swing.JFrame;
import org.jfree.chart.*;
import org.jfree.chart.axis.NumberAxis;
import org.jfree.chart.axis.NumberTickUnit;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.XYLineAndShapeRenderer;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;
import org.jfree.util.ShapeUtilities;

/**
 * @see http://stackoverflow.com/a/20359200/230513
 * @see http://stackoverflow.com/a/6669529/230513
 */
public class ScatterShape extends JFrame {

    private static final int N = 8;
    private static final int SIZE = 345;
    private static final String title = "Scatter Shape Demo";
    private static final Random rand = new Random();
    private final XYSeries series = new XYSeries("Data");

    public ScatterShape(String s) {
        super(s);
        final ChartPanel chartPanel = createDemoPanel();
        this.add(chartPanel, BorderLayout.CENTER);
    }

    private ChartPanel createDemoPanel() {
        JFreeChart chart = ChartFactory.createScatterPlot(
            title, "X", "Y", createSampleData(),
            PlotOrientation.VERTICAL, true, true, false);
        XYPlot xyPlot = (XYPlot) chart.getPlot();
        xyPlot.setDomainCrosshairVisible(true);
        xyPlot.setRangeCrosshairVisible(true);
        xyPlot.setRenderer(new XYLineAndShapeRenderer(false, true) {

            @Override
            public Shape getItemShape(int row, int col) {
                if (row == 0 & col == N) {
                    return ShapeUtilities.createDiagonalCross(5, 2);
                } else {
                    return super.getItemShape(row, col);
                }
            }
        });
        adjustAxis((NumberAxis) xyPlot.getDomainAxis(), true);
        adjustAxis((NumberAxis) xyPlot.getRangeAxis(), false);
        xyPlot.setBackgroundPaint(Color.white);
        return new ChartPanel(chart) {

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(SIZE, SIZE);
            }
        };
    }

    private void adjustAxis(NumberAxis axis, boolean vertical) {
        axis.setRange(-3.0, 3.0);
        axis.setTickUnit(new NumberTickUnit(0.5));
        axis.setVerticalTickLabels(vertical);
    }

    private XYDataset createSampleData() {
        XYSeriesCollection xySeriesCollection = new XYSeriesCollection();
        for (int i = 0; i < N * N; i++) {
            series.add(rand.nextGaussian(), rand.nextGaussian());
        }
        xySeriesCollection.addSeries(series);
        return xySeriesCollection;
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                ScatterShape demo = new ScatterShape(title);
                demo.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                demo.pack();
                demo.setLocationRelativeTo(null);
                demo.setVisible(true);
            }
        });
    }
}