实时图绘制开始时间

Question

这是基于@trashgod的有关实时绘图的示例的代码：

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);
        }
    });
}
}

运行Java之后，尽管new Seconds从0开始，但是我仍然不明白为什么图形从40秒开始？遍历代码；找不到任何要在40秒后开始的设置。

另外，如何向后滚动图形以查看以前的数据。

Answer 1

该图在构造Second传递到的日期的午夜之后的16分40秒处开始setTimeBase()。这是在nMoments构造函数参数中指定的相同的1000个间隔，每个间隔一秒。在给定的时间设置为午夜的情况下，获取基于零的显示的一些可能选择。

1. 使nMoments的整数倍60。

   dataset = new DynamicTimeSeriesCollection(1, 960, new Second());
   

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

2. 减去nMoments名义基准日期。

   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.