how to change dot shape with jfree polar plot?

I would like to know what are the methods to use to change dots polarplot size and shape . And also if it's possible to disable dots for this type of plot .

here is the code plotting polar of two series with default dots.

Thank you

package jfreechart;

import java.awt.Color;
import javax.swing.JFrame;

import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PolarPlot;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;

public class JFreeChartPolarChartExample extends JFrame {

   private static final long serialVersionUID = 1L;

   public JFreeChartPolarChartExample(String applicationTitle) {
       super(applicationTitle);
       XYSeriesCollection  dataSet = new XYSeriesCollection();
       
       XYSeries series1 = createRandomData("Series 1", 500);
       XYSeries series2 = createRandomData("Series 2", 60);
  
       dataSet.addSeries(series1);
       dataSet.addSeries(series2);
   
      PolarPlot pp = new PolarPlot();
      pp.setAngleGridlinePaint (Color.BLACK);
       
       JFreeChart polarChart = ChartFactory.createPolarChart(null, dataSet, true, true, false);

       // Adding chart into a chart panel
       ChartPanel chartPanel = new ChartPanel(polarChart);
  
       // settind default size
       chartPanel.setPreferredSize(new java.awt.Dimension(500, 270));
     
       setContentPane(chartPanel);
   
   }

   private static XYSeries createRandomData(final String name, final double maxvalue ) {
       final XYSeries series = new XYSeries(name);
       for (double az = 0.0; az < 360.0; az =az+10*Math.random()) 
       {
           final double value = maxvalue*(0.8 +0.2*Math.random());
           series.add(az, value);
       }
       return series;
   }

   public static void main(String[] args) {
       JFreeChartPolarChartExample chart = new JFreeChartPolarChartExample(null);
       chart.pack();
       chart.setVisible(true);
   }
}

Solution

with it, default dots are square.

Yes, the DefaultPolarItemRenderer uses a 6 x 6 square DEFAULT_SHAPE:

public static final Shape DEFAULT_SHAPE =
   new Rectangle2D.Double(-3.0, -3.0, 6.0, 6.0);

how to [make] them round and smaller?

As suggested here, use a custom DrawingSupplier. In the example below, the default Shape for all series is set to a circle of radius 2.5. ShapeUtils, shown in a comment, may also be useful:

DefaultPolarItemRenderer renderer = (DefaultPolarItemRenderer) polarPlot.getRenderer();
renderer.setAutoPopulateSeriesShape(false);
renderer.setDefaultShape(new Ellipse2D.Double(-2, -2, 5, 5));
//renderer.setDefaultShape(ShapeUtils.createDiamond(3));

how to disabled them?

Invoke setShapesVisible() as warranted:

renderer.setShapesVisible(true);

In addition,

You can zoom the chart radially as shown here.
Instead of making a new PolarPlot(), get the one instantiated by the chart's factory.
To establish the chart's initial size, override getPreferredSize(), as suggested here.
Use (nearly) equal width and height to maximize the plot in the enclosing container.
Construct and manipulate Swing GUI objects only on the event dispatch thread.

As tested:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.geom.Ellipse2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.NumberAxis;
import org.jfree.chart.axis.NumberTickUnit;
import org.jfree.chart.plot.PolarPlot;
import org.jfree.chart.renderer.DefaultPolarItemRenderer;
import org.jfree.chart.util.ShapeUtils;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;

/**
 * @see https://stackoverflow.com/q/71632468/230513
 * @see https://stackoverflow.com/a/46931762/230513
 */
public class Skyplot {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Skyplot()::plot);
    }

    private void plot() {
        JFrame plotFrame = new JFrame("PolarPlot");
        plotFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        plotFrame.add(new Plotter());
        plotFrame.pack();
        plotFrame.setLocationRelativeTo(null);
        plotFrame.setVisible(true);
    }

    private static final class Plotter extends JPanel {

        public Plotter() {
            super(new GridLayout());
            this.add(createChartPanel(getXYDataset()));
        }

        private ChartPanel createChartPanel(XYDataset dataset) {
            JFreeChart chart = ChartFactory.createPolarChart(
                "Random Data", dataset, true, true, false);

            PolarPlot polarPlot = (PolarPlot) chart.getPlot();
            polarPlot.setAngleGridlinePaint (Color.BLACK);
            polarPlot.setRadiusGridlinePaint(Color.BLACK);

            DefaultPolarItemRenderer renderer = (DefaultPolarItemRenderer) polarPlot.getRenderer();
            renderer.setAutoPopulateSeriesShape(false);
            renderer.setDefaultShape(new Ellipse2D.Double(-2, -2, 5, 5));
            //renderer.setDefaultShape(ShapeUtils.createDiamond(3));
            renderer.setShapesVisible(true);

            NumberAxis rangeAxis = (NumberAxis) polarPlot.getAxis();
            rangeAxis.setTickUnit(new NumberTickUnit(100.0));

            return new ChartPanel(chart) {
                @Override
                public Dimension getPreferredSize() {
                    return new Dimension(500, 500);
                }
            };
        }

        private XYDataset getXYDataset() {
            XYSeriesCollection dataset = new XYSeriesCollection();
            dataset.addSeries(createRandomData("Series 1", 500));
            dataset.addSeries(createRandomData("Series 2", 60));
            return dataset;
        }

        private static XYSeries createRandomData(final String name, final double maxvalue) {
            final XYSeries series = new XYSeries(name);
            for (double az = 0.0; az < 360.0; az = az + 10 * Math.random()) {
                final double value = maxvalue * (0.8 + 0.2 * Math.random());
                series.add(az, value);
            }
            return series;
        }
    }
}