Andrew E. Bruno

In my previous post I discussed a tool called mif2xml for converting MIF files to an intermediate XML dialect. In this post I’ll talk about the Java port of mif2xml called mif2xml-j which you can download here including just the executable jar.

JFlex is a lexical analyzer generator for Java and is the library I chose to use for creating the MIF lexer. The first step was to get JFlex integrated into my build environment. For this project I decided to use ant but integrating JFlex into another build environment Read the rest of this entry »

Sparklines are very small charts usually displayed along side some text and help quickly compare time series data. They are usually rendered without any axis, labels, or tick marks and appear as just a simple line. Sparklines were developed by Edward Tufte and further explained here.

JFreeChart does not have any built in classes for creating sparklines but are easily created by adjusting a few settings in the basic charting classes. Here’s a few quick examples of some sparklines generated using JFreeChart:

Foo 90
Bar 34
Baz 54

To create sparklines using JFreeChart you just need to turn off the display of labels, tickmarks, lines, etc. on the domain/range axis as well as the XYPlot.

Here’s a complete example:

import java.io.File;
import java.io.IOException;
import java.util.Calendar;
import java.util.Date;
import java.util.Random;

import org.jfree.chart.ChartUtilities;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.DateAxis;
import org.jfree.chart.axis.DateTickUnit;
import org.jfree.chart.axis.NumberAxis;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.StandardXYItemRenderer;
import org.jfree.data.time.Day;
import org.jfree.data.time.TimeSeries;
import org.jfree.data.time.TimeSeriesCollection;
import org.jfree.ui.RectangleInsets;

public class Sparkline {
    public static void main(String[] args) {
        TimeSeriesCollection dataSet = new TimeSeriesCollection();
        Day day = new Day();
        TimeSeries data = new TimeSeries("Sparkline", day.getClass());

        // XXX add real data here
        Random r = new Random();
        Calendar c = Calendar.getInstance();
        for(int i = 0; i < 100; i++) {
            int val = r.nextInt(100);
            if(val < 50)
                val += 50;
            c.add(Calendar.DATE, 7);
            Date date = c.getTime();
            data.add(new Day(date), val);
        }

        dataSet.addSeries(data);

        // The sparkline is created by setting a bunch of the visible properties
        // on the domain, range axis and the XYPlot to false
        DateAxis x = new DateAxis();
        x.setTickUnit(new DateTickUnit(DateTickUnit.MONTH, 1));
        x.setTickLabelsVisible(false);
        x.setTickMarksVisible(false);
        x.setAxisLineVisible(false);
        x.setNegativeArrowVisible(false);
        x.setPositiveArrowVisible(false);
        x.setVisible(false);

        NumberAxis y = new NumberAxis();
        y.setTickLabelsVisible(false);
        y.setTickMarksVisible(false);
        y.setAxisLineVisible(false);
        y.setNegativeArrowVisible(false);
        y.setPositiveArrowVisible(false);
        y.setVisible(false);

        XYPlot plot = new XYPlot();
        plot.setInsets(new RectangleInsets(-1, -1, 0, 0));
        plot.setDataset(dataSet);
        plot.setDomainAxis(x);
        plot.setDomainGridlinesVisible(false);
        plot.setDomainCrosshairVisible(false);
        plot.setRangeGridlinesVisible(false);
        plot.setRangeCrosshairVisible(false);
        plot.setRangeAxis(y);
        plot.setRenderer(new StandardXYItemRenderer(
                StandardXYItemRenderer.LINES));

        JFreeChart chart = new JFreeChart(null, JFreeChart.DEFAULT_TITLE_FONT,
                plot, false);
        chart.setBorderVisible(false);

        try {
            ChartUtilities.saveChartAsPNG(new File("sparkline.png"), chart,
                    100, 30);
        } catch(IOException e) {
            System.err.println("Failed to render chart as png: "
                    + e.getMessage());
            e.printStackTrace();
        }
    }
}