Jfreechart Boxplot DefaultBoxAndWhiskerCategoryDataset initialization

Question

I want to draw a simple boxplot(Box and whisker plot) with some data from the user (1 boxplot not many) and I'm having problem with the DefaultBoxAndWhiskerCategoryDataset Variable in jfreechart. it seems that whatever data I enter just vanishes. the plot is always a triangle instead of a boxplot

package boxplot;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.CategoryAxis;
import org.jfree.chart.axis.NumberAxis;
import org.jfree.chart.labels.BoxAndWhiskerToolTipGenerator;
import org.jfree.chart.plot.CategoryPlot;
import org.jfree.chart.renderer.category.BoxAndWhiskerRenderer;
import org.jfree.data.statistics.BoxAndWhiskerCategoryDataset;
import org.jfree.data.statistics.DefaultBoxAndWhiskerCategoryDataset;
import org.jfree.ui.ApplicationFrame;
import org.jfree.ui.RefineryUtilities;


public class Boxplot extends ApplicationFrame{

    @SuppressWarnings("deprecation")
    public Boxplot(String title) {
        super(title);

        final BoxAndWhiskerCategoryDataset dataset = createDataset();

        final CategoryAxis xAxis = new CategoryAxis("");
        final NumberAxis yAxis = new NumberAxis("Value");
        yAxis.setAutoRangeIncludesZero(false);
        final BoxAndWhiskerRenderer renderer = new BoxAndWhiskerRenderer();
        renderer.setFillBox(false);
        renderer.setToolTipGenerator(new BoxAndWhiskerToolTipGenerator());
        final CategoryPlot plot = new CategoryPlot(dataset, xAxis, yAxis, renderer);

        final JFreeChart chart = new JFreeChart(
            "Box-and-Whisker Demo",
            plot
        );
        final ChartPanel chartPanel = new ChartPanel(chart);
        chartPanel.setPreferredSize(new java.awt.Dimension(450, 270));
        setContentPane(chartPanel);

    }

    public static void main(String[] args) {

        final Boxplot plot = new Boxplot("");
        plot.pack();
        RefineryUtilities.centerFrameOnScreen(plot);
        plot.setVisible(true);
    }

    private static DefaultBoxAndWhiskerCategoryDataset createDataset() {
        System.out.print("Input the data (use space after every input)");

        double[] inputData =  getInputData();

        ArrayList<Double> inputDataList = new ArrayList<Double>();
        for (int i=0;i<100;i++)
            inputDataList.add(i, inputData[i]);

        final DefaultBoxAndWhiskerCategoryDataset dataset 
            = new DefaultBoxAndWhiskerCategoryDataset();
        dataset.add(inputDataList, "1", "2");

        return dataset;
    }

    private static double[] getInputData() {
        Scanner scanner = new Scanner(System.in);

        double[] data = new double[100];
        Arrays.fill(data, -1);

        int index =0;
        do
        {
            double temp = scanner.nextDouble();
            if (temp==-1)
                break;
            data[index++]= temp;
        }while (scanner.hasNext());
        scanner.close();

        return data;
    }

}

Answer 1

It's not clear where your example fails. Your recapitulation of the relevant factory method, ChartFactory.createBoxAndWhiskerChart() shown here, appears correct. It may be easier to start with a simpler working example. Some notes:

• For convenience, I've constructed a Scanner using a String, rather than System.in.

• I've also simplified getInputData() to return to a List<Number>, which is suitable for the dataset's add() method.

• Swing GUI objects should be constructed and manipulated only on the event dispatch thread.

• Don't use setPreferredSize() when you really mean to override getPreferredSize(). as discussed here.

import java.awt.Dimension;
import java.awt.EventQueue;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import javax.swing.JFrame;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.data.statistics.DefaultBoxAndWhiskerCategoryDataset;

/**
 * @see https://stackoverflow.com/a/35814571/230513
 */
public class BoxPlot {

    private static final String ROW_KEY = "City";

    private void display() {
        JFrame f = new JFrame("BoxPlot");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        DefaultBoxAndWhiskerCategoryDataset data = new DefaultBoxAndWhiskerCategoryDataset();
        data.add(getInputData(), ROW_KEY, "Coruscant");
        JFreeChart chart = ChartFactory.createBoxAndWhiskerChart(
            "Box and Whisker Chart", ROW_KEY, "Temperature", data, false);
        f.add(new ChartPanel(chart) {

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(320, 480);
            }
        });
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    private List<Number> getInputData() {
        Scanner s = new Scanner("30 36 46 55 65 76 81 80 71 59 44 34");
        List<Number> list = new ArrayList<>();
        do {
            list.add(s.nextDouble());
        } while (s.hasNext());
        return list;
    }

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