First Pie with JFreeChart

I have to generate charts from Java. Among the available possibility, JFreeChart has been chosen.
In this post I start from nothing to save a PNG with a pie chart in it.

Well, actually, I have something more than nothing, namely a windows box with Java 8 on it and Eclipse Neon as IDE. I create a Maven project, and I added a few dependencies. The most relevant here is the JFreeChart one, however, don't forget a test library, I'm using JUnit 4:

<dependency>
 <groupId>org.jfree</groupId>
 <artifactId>jfreechart</artifactId>
 <version>1.0.19</version>
</dependency>
<dependency>
 <groupId>junit</groupId>
 <artifactId>junit</artifactId>
 <version>4.12</version>
 <scope>test</scope>
</dependency>

I want to explore how to create pie charts, so I create a class Pie in a chart package with a static method in it, createSimple() that would return true if the process succeed.

package chart;

public class Pie {
    static boolean createSimple() {
        return false;
    }
}

Then I create a test case, that is going to be quite trivial, but at least clearly split the concern about writing the code and testing it in two different places. The alternative, giving a main function to the Pie class would have been more regrettable.

@Test
public void testCreate() {
    assertTrue(Pie.createSimple());
}

So, let's create a pie reporting a few elements in it, defined by a name and an associated value. We are going to use all the possible default provided, just to have a picture to display.

DefaultPieDataset dataset = new DefaultPieDataset(); // 1
dataset.setValue("Merlin", 2.50);
dataset.setValue("Tiger", 18.27);
dataset.setValue("Mustang", 41.33);
dataset.setValue("Dolphin", 72.02);

JFreeChart chart = ChartFactory.createPieChart("Versions", dataset); // 2

1. I create dataset, and I push a few description/value couples to it.
2. Then I create a pie chart going through the ChartFactory class. As parameter, this factory method requires just the name I want to give the chart and the data it should use to create it.

I want to put the image in a file, in the PNG format. This is easily done.

try {
    ChartUtilities.saveChartAsPNG(new File("dump/pie.png"), chart, 500, 500);
    return true;
} catch(IOException ioe) {
    log.error(ioe.getMessage());
    return false;
}

Be careful of passing to saveChartAsPNG() a file that could be created. If the path does not exist, you are going to get an exception. The other parameters are the chart that has to be created, and its size, width x height. Here is the result I've got:

Nice. However, I'd like not to see the tooltips. From the documentation, I read that I can have a better control on the generated picture calling the overload of createPieChart() that accepts three boolean more, ruling the display of legend, tooltips, and URLs. The shorter version I used above is equivalent to:

// legend and tooltips
JFreeChart chart = ChartFactory.createPieChart("Languages", dataset, true, true, false);

So we just set the second boolean to false to get rid of the tooltips, right? Well, not. For same strange reason, that flag does not work. Fortunately there is a workaround, we can disable the label generator.

// disable tooltips not working!
JFreeChart chart = ChartFactory.createPieChart("Versions", dataset, true, false, false);

PiePlot pp = (PiePlot) chart.getPlot();
// force tooltips off
pp.setLabelGenerator(null);

Try commenting the call to setLabelGenerator(), you will still see the tooltips on the pie, otherwise you'll have only the legend.

Say that I don't like the default color choice, and I want the Mustang slice in magenta. I can call setSectionPaint() on the PiePlot for that slice to change it:

pp.setSectionPaint("Mustang", Color.MAGENTA);

Notice that magenta replaced green for Mustang, but green is not out of the game, it has merely shifted to the next slice.

Last change I want to do here, let also the legend off:

JFreeChart chart = ChartFactory.createPieChart("Versions", dataset, false, false, false);

I have pushed the project on GitHub.