How to change the color of multiple ellipses using a loop (JFreeChart)

Question

I have drawn multiple ellipses using a loop as shown below, and the results are perfect using one color for all the ellipses, but my target is to color each ellipse with differ

Answer 1

tens of XYShapeAnnotations will be created…so creating multiple instances of XYShapeAnnotation will not work for my purpose.

Happily, an instance XYShapeAnnotation is small—just 48 bytes each in the example below. You'll want to profile to be sure.

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.geom.Ellipse2D;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartFrame;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.annotations.XYShapeAnnotation;
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;

/**
 * @see https://stackoverflow.com/a/35236100/230513
 */
public class AnnotationTest {

    private static final BasicStroke stroke = new BasicStroke(2.0f);
    private static final int N = 16;
    private static final int S = 8;

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

    private void display() {
        XYDataset data = createDataset();
        JFreeChart chart = ChartFactory.createXYLineChart("ArcTest", "X", "Y",
            data, PlotOrientation.VERTICAL, true, true, false);
        XYPlot plot = chart.getXYPlot();
        XYLineAndShapeRenderer renderer
            = (XYLineAndShapeRenderer) plot.getRenderer();
        renderer.setBaseShapesVisible(true);
        for (int i = 0; i < N; i++) {
            double x = data.getXValue(0, i) - S / 2;
            double y = data.getYValue(0, i) - S / 2;
            Ellipse2D.Double ellipse = new Ellipse2D.Double(x, y, S, S);
            Color color = Color.getHSBColor((float) i / N, 1, 1);
            renderer.addAnnotation(new XYShapeAnnotation(ellipse, stroke, color));
        }
        ChartFrame frame = new ChartFrame("Test", chart);
        frame.pack();
        frame.setVisible(true);
    }

    private static XYDataset createDataset() {
        XYSeriesCollection result = new XYSeriesCollection();
        XYSeries series = new XYSeries("ArcTest");
        for (int i = 0; i < N; i++) {
            series.add(i * S, i * S);
        }
        result.addSeries(series);
        return result;
    }
}