Real time graph plotting starting time

Question

Here is code based on @trashgod's example about real time plotting:

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.SimpleDateFormat;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.DateAxis;
import org.jfree.chart.plot.XYPlot;
import org.jfree.data.time.DynamicTimeSeriesCollection;
import org.jfree.data.time.Second;

/**
 * @see https://stackoverflow.com/a/21307289/230513
 */
public class DynamicTimeSeriesChart extends JPanel {

private static final long serialVersionUID = 5128935838291298041L;
private final DynamicTimeSeriesCollection dataset;
private final JFreeChart chart;

public DynamicTimeSeriesChart(final String title) {
    dataset = new DynamicTimeSeriesCollection(1, 1000, new Second());
    dataset.setTimeBase(new Second(0, 0, 0, 1, 1, 2014));
    dataset.addSeries(new float[1], 0, title);
    chart = ChartFactory.createTimeSeriesChart(
        title, "Time", title, dataset, true, true, false);
    final XYPlot plot = chart.getXYPlot();
    DateAxis axis = (DateAxis) plot.getDomainAxis();
    axis.setFixedAutoRange(10000);
    axis.setDateFormatOverride(new SimpleDateFormat("ss.SS"));
    final ChartPanel chartPanel = new ChartPanel(chart);
    add(chartPanel);
}

public void update(float value) {
    float[] newData = new float[1];
    newData[0] = value;
    dataset.advanceTime();
    dataset.appendData(newData);
}

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {

        @Override
        public void run() {
            JFrame frame = new JFrame("testing");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            final DynamicTimeSeriesChart chart
                = new DynamicTimeSeriesChart("Alternating data");
            frame.add(chart);
            frame.pack();
            Timer timer = new Timer(1000, new ActionListener() {
                private boolean b;

                @Override
                public void actionPerformed(ActionEvent e) {
                    chart.update(b ? 1 : 0);
                    b = !b;
                }
            });
            timer.start();
            frame.setVisible(true);
        }
    });
}
}

After running the Java, I still don't understand why the graph starts at 40 seconds, although the new Seconds start from 0? Ran through code; can't find any settings to start at 40 seconds.

Also, how to scroll back graph to see previous data.

Answer 1

The graph starts at 16 minutes and 40 seconds after midnight on the date used to construct the Second passed to setTimeBase(). This is the same 1000 intervals, each one second long, specified in the nMoments constructor parameter. Some possible alternatives to get a zero-based display, given a time set to midnight.

1. Make nMoments a multiple of 60.

   dataset = new DynamicTimeSeriesCollection(1, 960, new Second());
   dataset.setTimeBase(new Second(0, 0, 0, 1, 1, 2014));
   

2. Subtract nMoments from the nominal base date.

   int nMoments = 1000;
   dataset = new DynamicTimeSeriesCollection(1, nMoments, new Second());
   Calendar c = Calendar.getInstance();
   c.setTime(new Date(0));
   c.add(Calendar.SECOND, -nMoments);
   dataset.setTimeBase(new Second(c.getTime()));
   

Either approach yields the same display.