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In JFreeChart how to get the [x,y] values of a certain point on the chart?

由 爱⌒轻易说出口 提交于 2021-01-07 03:15:30

问题


This question is related to my previous question [ How to display volume in the domain crosshair and set the crosshair programmatically? ], with the help of @trashgod, I got the answers for most of my questions, but one question is still unanswered, here I'll ask this question from a different angle.

In my Swing app, there is a list of dates with some data, when I click on a certain date, I want my app to display a chart and points to that date when the image shows up, so I don't have to move my mouse around to find and display info of that date. So the app screen shots look like the following.

So as you can see from the top screenshot, if I click on 2020-07-29 on the date list, the chart will load and the cross-hairs will be automatically focused on 2020-07-29, and the relative info will auto show up. In the bottom screenshot, if I click on the date 2020-08-11, the chart image will load and the mouse will be set on 2020-08-11, so as a user, I don't have to search on the image and find that date's data.

My simplified app is listed below :

import java.awt.*;
import java.awt.event.*;
import java.text.*;
import java.util.*;
import javax.swing.*;
import org.jfree.chart.*;
import org.jfree.chart.axis.*;
import org.jfree.chart.entity.*;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.XYBarRenderer;
import org.jfree.data.time.*;
import org.jfree.data.xy.XYDataset;
import org.jfree.chart.labels.*;
import org.jfree.chart.panel.*;
import org.jfree.chart.plot.*;

public class PriceVolume_Chart extends JPanel implements ChartMouseListener    // A demo application for price-volume chart.   
{
  ChartPanel panel;
  TimeSeries Price_series=new TimeSeries("Price");
  TimeSeries Volume_Series=new TimeSeries("Volume");
  Crosshair xCrosshair,yCrosshair;
  static Vector<String> Volume_Color_Vector=new Vector();

  public PriceVolume_Chart(String Symbol)
  {
    JFreeChart chart=createChart(Symbol);
    panel=new ChartPanel(chart,true,true,true,false,true);
    panel.setPreferredSize(new Dimension(1000,500));
    panel.addChartMouseListener(this);
    CrosshairOverlay crosshairOverlay=new CrosshairOverlay();
    float[] dash={2f,0f,2f};
    BasicStroke bs=new BasicStroke(1,BasicStroke.CAP_BUTT,BasicStroke.JOIN_ROUND,1.0f,dash,2f);

    xCrosshair=new Crosshair(Double.NaN,Color.GRAY,bs);
    xCrosshair.setLabelBackgroundPaint(new Color(0f,0f,0f,1f));
    xCrosshair.setLabelFont(xCrosshair.getLabelFont().deriveFont(14f));
    xCrosshair.setLabelPaint(new Color(1f,1f,1f,1f));
    
    xCrosshair.setLabelGenerator(new CrosshairLabelGenerator()
    {
      @Override
      public String generateLabel(Crosshair crosshair)
      {
        long ms=(long)crosshair.getValue();
        TimeSeriesDataItem item=null;
        for (int i=0;i<Volume_Series.getItemCount();i++)
        {
          item=Volume_Series.getDataItem(i);
          if (ms==item.getPeriod().getFirstMillisecond()) break;
        }
        long volume=item.getValue().longValue();
        return NumberFormat.getInstance().format(volume);
      }
    });

    xCrosshair.setLabelVisible(true);
    yCrosshair=new Crosshair(Double.NaN,Color.GRAY,bs);
    yCrosshair.setLabelBackgroundPaint(new Color(0f,0f,0f,1f));
    yCrosshair.setLabelFont(xCrosshair.getLabelFont().deriveFont(14f));
    yCrosshair.setLabelPaint(new Color(1f,1f,1f,1f));
    yCrosshair.setLabelVisible(true);
    crosshairOverlay.addDomainCrosshair(xCrosshair);
    crosshairOverlay.addRangeCrosshair(yCrosshair);
    panel.addOverlay(crosshairOverlay);
    add(panel);
/*
    xCrosshair.setValue(1.5959952E12);
    xCrosshair.setVisible(true);
    yCrosshair.setValue(45.230579);
    yCrosshair.setVisible(true);
*/
  }

  private JFreeChart createChart(String Symbol)
  {
    createPriceDataset(Symbol);
    XYDataset priceData=new TimeSeriesCollection(Price_series);
    JFreeChart chart=ChartFactory.createTimeSeriesChart(Symbol,"Date",getYLabel("Price ( $ )"),priceData,true,true,true);
    XYPlot plot=chart.getXYPlot();
    plot.setBackgroundPaint(new Color(192,196,196));
    NumberAxis rangeAxis1=(NumberAxis)plot.getRangeAxis();
    rangeAxis1.setLowerMargin(0.40);                                           // Leave room for volume bars
    plot.getRenderer().setDefaultToolTipGenerator(new StandardXYToolTipGenerator(StandardXYToolTipGenerator.DEFAULT_TOOL_TIP_FORMAT,new SimpleDateFormat("yyyy-MM-d"),NumberFormat.getCurrencyInstance()));

    NumberAxis rangeAxis2=new NumberAxis("Volume");
    rangeAxis2.setUpperMargin(1.00);                                           // Leave room for price line   
    rangeAxis2.setNumberFormatOverride(NumberFormat.getNumberInstance());
    plot.setRangeAxis(1,rangeAxis2);
    plot.setDataset(1,new TimeSeriesCollection(Volume_Series));
    plot.setRangeAxis(1,rangeAxis2);
    plot.mapDatasetToRangeAxis(1,1);
    MyRender Renderer=new MyRender();
    Renderer.setShadowVisible(false);
    plot.setRenderer(1,Renderer);

    DateAxis domainAxis=(DateAxis) plot.getDomainAxis();                     // Consider adjusting the lower margin of the domain axis for symmetry.
    domainAxis.setLowerMargin(0.05);

    return chart;
  }

  private void createPriceDataset(String Symbol)
  {
    String Lines[]=new String[21],Items[],Date;
    int Year, Month, Day;
    long Volume,Last_Volume=0;
    double Price;

    Lines[0]="Date,Open,High,Low,Close,Adj Close,Volume";
    Lines[1]="2020-07-17,44.110001,44.369999,41.919998,42.509998,42.323395,849700";
    Lines[2]="2020-07-20,41.630001,41.680000,39.669998,40.119999,39.943886,1319300";
    Lines[3]="2020-07-21,40.880001,42.860001,40.860001,42.270000,42.084450,2070300";
    Lines[4]="2020-07-22,41.919998,42.700001,41.090000,42.570000,42.383133,1317600";
    Lines[5]="2020-07-23,43.919998,46.389999,43.279999,44.759998,44.563519,1917700";
    Lines[6]="2020-07-24,46.500000,46.500000,43.950001,44.410000,44.215057,1384600";
    Lines[7]="2020-07-27,44.000000,44.240002,42.610001,43.860001,43.667469,799800";
    Lines[8]="2020-07-28,43.389999,44.590000,42.930000,43.020000,42.831158,699700";
    Lines[9]="2020-07-29,42.759998,45.590000,42.740002,45.430000,45.230579,826200";
    Lines[10]="2020-07-30,44.160000,44.639999,42.959999,44.500000,44.304661,798100";
    Lines[11]="2020-07-31,44.330002,44.419998,42.580002,44.360001,44.165276,1037800";
    Lines[12]="2020-08-03,44.560001,45.599998,43.419998,44.939999,44.742729,797000";
    Lines[13]="2020-08-04,44.900002,45.500000,43.450001,43.540001,43.348877,971100";
    Lines[14]="2020-08-05,44.860001,45.389999,43.650002,45.330002,45.131020,902000";
    Lines[15]="2020-08-06,45.049999,46.279999,44.330002,45.299999,45.101147,645200";
    Lines[16]="2020-08-07,44.849998,46.189999,44.189999,46.150002,45.947418,604900";
    Lines[17]="2020-08-10,46.669998,48.410000,46.549999,47.290001,47.082417,960200";
    Lines[18]="2020-08-11,49.110001,50.849998,48.799999,48.910000,48.695301,1187700";
    Lines[19]="2020-08-12,49.759998,50.009998,47.060001,47.840000,47.630001,752800";
    Lines[20]="2020-08-13,46.950001,48.369999,46.459999,47.110001,47.110001,535700";

    for (int i=1;i<Lines.length;i++)
    {
      Items=Lines[i].split(",");
      Date=Items[0].replace("-0","-");
      Price=Double.parseDouble(Items[5]);
      Volume=Long.parseLong(Items[6]);
      Items=Date.split("-");
      Year=Integer.parseInt(Items[0]);
      Month=Integer.parseInt(Items[1]);
      Day=Integer.parseInt(Items[2]);
      Price_series.add(new Day(Day,Month,Year),Price);
      Volume_Series.add(new Day(Day,Month,Year),Volume);
      Volume_Color_Vector.add(Volume>=Last_Volume?"+":"-");
      Last_Volume=Volume;
    }
  }

  @Override
  public void chartMouseClicked(ChartMouseEvent event)
  {
    // ignore
  }

  public void chartMouseMoved(ChartMouseEvent cmevent)
  {
    ChartEntity chartentity=cmevent.getEntity();
    if (chartentity instanceof XYItemEntity)
    {
      XYItemEntity e=(XYItemEntity)chartentity;
      XYDataset d=e.getDataset();
      int s=e.getSeriesIndex();
      int i=e.getItem();
      double x=d.getXValue(s,i);
      double y=d.getYValue(s,i);
      Out("x = "+x+"  y = "+y);
      xCrosshair.setValue(x);
      yCrosshair.setValue(y);
    }
  }

  String getYLabel(String Text)
  {
    String Result="";

    for (int i=0;i<Text.length();i++) Result+=Text.charAt(i)+(i<Text.length()-1?"\u2009":"");
//    Out(Result);
    return Result;
  }

  private static void out(String message) { System.out.print(message); }

  private static void Out(String message) { System.out.println(message); }

  // Create the GUI and show it. For thread safety, this method should be invoked from the event-dispatching thread.
  static void Create_And_Show_GUI()
  {
    final PriceVolume_Chart demo=new PriceVolume_Chart("ADS");

    JFrame frame=new JFrame("PriceVolume_Chart Frame");
    frame.add(demo);
    frame.addWindowListener(new WindowAdapter()
    {
      public void windowActivated(WindowEvent e) { }
      public void windowClosed(WindowEvent e) { }
      public void windowClosing(WindowEvent e) { System.exit(0); }
      public void windowDeactivated(WindowEvent e) { }
      public void windowDeiconified(WindowEvent e) { demo.repaint(); }
      public void windowGainedFocus(WindowEvent e) { demo.repaint(); }
      public void windowIconified(WindowEvent e) { }
      public void windowLostFocus(WindowEvent e) { }
      public void windowOpening(WindowEvent e) { demo.repaint(); }
      public void windowOpened(WindowEvent e) { }
      public void windowResized(WindowEvent e) { demo.repaint(); }
      public void windowStateChanged(WindowEvent e) { demo.repaint(); }
    });
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }

  public static void main(String[] args)
  {
    // Schedule a job for the event-dispatching thread : creating and showing this application's GUI.
    SwingUtilities.invokeLater(new Runnable() { public void run() { Create_And_Show_GUI(); } });
  }
}

class MyRender extends XYBarRenderer
{
  @Override
  public Paint getItemPaint(int row,int col)
  {
    this.setBarAlignmentFactor(0.5);
//    System.out.println(row+" "+col+" "+super.getItemPaint(row,col));
    return PriceVolume_Chart.Volume_Color_Vector.elementAt(col).equals("+")?super.getItemPaint(row,col):new Color(0.56f,0.2f,0.5f,1f);
  }
}

I know how to set the cross-hair on a certain point on the chart [ Commented out : xCrosshair.setValue(1.5959952E12); ], yet I do not know the [x,y] values of a certain date on a certain chart, therefore my question is : on a JFreeChart like the one I have here, how to get the [x,y] values of a vertain date [ e.g. 2020-07-29 ], or how to get the [x,y] values of the N-th date [ e.g. 9-th date = 2020-07-29 ] ?


回答1:


Alright, @trashgod was inspirational. I finally tried his suggestions and got to the answer I was looking for; here is the essential solution:

TimeSeriesDataItem itemX = Volume_Series.getDataItem(Index);
xCrosshair.setValue(itemX.getPeriod().getFirstMillisecond());

TimeSeriesDataItem itemY = Price_series.getDataItem(Index);
yCrosshair.setValue(itemY.getValue().doubleValue());

Complete example:

import java.awt.*;
import java.awt.event.*;
import java.text.*;
import java.util.*;
import javax.swing.*;
import org.jfree.chart.*;
import org.jfree.chart.axis.*;
import org.jfree.chart.entity.*;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.XYBarRenderer;
import org.jfree.data.time.*;
import org.jfree.data.xy.XYDataset;
import org.jfree.chart.labels.*;
import org.jfree.chart.panel.*;
import org.jfree.chart.plot.*;

public class PriceVolume_Chart extends JPanel implements ChartMouseListener   // A demo application for price-volume chart.   
{
  ChartPanel panel;
  TimeSeries Price_series=new TimeSeries("Price");
  TimeSeries Volume_Series=new TimeSeries("Volume");
  Crosshair xCrosshair,yCrosshair;
  static Vector<String> Volume_Color_Vector=new Vector();
  private int index;

  public PriceVolume_Chart(String Symbol,int Index)
  {
    JFreeChart chart=createChart(Symbol);
    panel=new ChartPanel(chart,true,true,true,false,true);
    panel.setPreferredSize(new Dimension(1000,500));
    panel.addChartMouseListener(this);
    CrosshairOverlay crosshairOverlay=new CrosshairOverlay();
    float[] dash={2f,0f,2f};
    BasicStroke bs=new BasicStroke(1,BasicStroke.CAP_BUTT,BasicStroke.JOIN_ROUND,1.0f,dash,2f);

    xCrosshair=new Crosshair(Double.NaN,Color.GRAY,bs);
    xCrosshair.setLabelBackgroundPaint(new Color(0f,0f,0f,1f));
    xCrosshair.setLabelFont(xCrosshair.getLabelFont().deriveFont(14f));
    xCrosshair.setLabelPaint(new Color(1f,1f,1f,1f));
    
    xCrosshair.setLabelGenerator(new CrosshairLabelGenerator()
    {
      @Override
      public String generateLabel(Crosshair crosshair)
      {
        long ms=(long)crosshair.getValue();
        TimeSeriesDataItem item=null;
        for (int i=0;i<Volume_Series.getItemCount();i++)
        {
          item=Volume_Series.getDataItem(i);
          if (ms==item.getPeriod().getFirstMillisecond()) break;
        }
        long volume=item.getValue().longValue();
        return NumberFormat.getInstance().format(volume);
      }
    });

    xCrosshair.setLabelVisible(true);
    yCrosshair=new Crosshair(Double.NaN,Color.GRAY,bs);
    yCrosshair.setLabelBackgroundPaint(new Color(0f,0f,0f,1f));
    yCrosshair.setLabelFont(xCrosshair.getLabelFont().deriveFont(14f));
    yCrosshair.setLabelPaint(new Color(1f,1f,1f,1f));
    yCrosshair.setLabelVisible(true);
    crosshairOverlay.addDomainCrosshair(xCrosshair);
    crosshairOverlay.addRangeCrosshair(yCrosshair);
    panel.addOverlay(crosshairOverlay);
    add(panel);
    
    TimeSeriesDataItem itemX=Volume_Series.getDataItem(Index);
    xCrosshair.setValue(itemX.getPeriod().getFirstMillisecond());
    
    TimeSeriesDataItem itemY=Price_series.getDataItem(Index);
    yCrosshair.setValue(itemY.getValue().doubleValue());
  }

  private JFreeChart createChart(String Symbol)
  {
    createPriceDataset(Symbol);
    XYDataset priceData=new TimeSeriesCollection(Price_series);
    JFreeChart chart=ChartFactory.createTimeSeriesChart(Symbol,"Date",getYLabel("Price ( $ )"),priceData,true,true,true);
    XYPlot plot=chart.getXYPlot();
    plot.setBackgroundPaint(new Color(192,196,196));
    NumberAxis rangeAxis1=(NumberAxis)plot.getRangeAxis();
    rangeAxis1.setLowerMargin(0.40);                                           // Leave room for volume bars
    plot.getRenderer().setDefaultToolTipGenerator(new StandardXYToolTipGenerator(StandardXYToolTipGenerator.DEFAULT_TOOL_TIP_FORMAT,new SimpleDateFormat("yyyy-MM-d"),NumberFormat.getCurrencyInstance()));

    NumberAxis rangeAxis2=new NumberAxis("Volume");
    rangeAxis2.setUpperMargin(1.00);                                           // Leave room for price line   
    rangeAxis2.setNumberFormatOverride(NumberFormat.getNumberInstance());
    plot.setRangeAxis(1,rangeAxis2);
    plot.setDataset(1,new TimeSeriesCollection(Volume_Series));
    plot.setRangeAxis(1,rangeAxis2);
    plot.mapDatasetToRangeAxis(1,1);
    MyRender Renderer=new MyRender();
    Renderer.setShadowVisible(false);
    plot.setRenderer(1,Renderer);

    DateAxis domainAxis=(DateAxis) plot.getDomainAxis();                     // Consider adjusting the lower margin of the domain axis for symmetry.
    domainAxis.setLowerMargin(0.05);

    return chart;
  }

  private void createPriceDataset(String Symbol)
  {
    String Lines[]=new String[21],Items[],Date;
    int Year, Month, Day;
    long Volume,Last_Volume=0;
    double Price;

    Lines[0]="Date,Open,High,Low,Close,Adj Close,Volume";
    Lines[1]="2020-07-17,44.110001,44.369999,41.919998,42.509998,42.323395,849700";
    Lines[2]="2020-07-20,41.630001,41.680000,39.669998,40.119999,39.943886,1319300";
    Lines[3]="2020-07-21,40.880001,42.860001,40.860001,42.270000,42.084450,2070300";
    Lines[4]="2020-07-22,41.919998,42.700001,41.090000,42.570000,42.383133,1317600";
    Lines[5]="2020-07-23,43.919998,46.389999,43.279999,44.759998,44.563519,1917700";
    Lines[6]="2020-07-24,46.500000,46.500000,43.950001,44.410000,44.215057,1384600";
    Lines[7]="2020-07-27,44.000000,44.240002,42.610001,43.860001,43.667469,799800";
    Lines[8]="2020-07-28,43.389999,44.590000,42.930000,43.020000,42.831158,699700";
    Lines[9]="2020-07-29,42.759998,45.590000,42.740002,45.430000,45.230579,826200";
    Lines[10]="2020-07-30,44.160000,44.639999,42.959999,44.500000,44.304661,798100";
    Lines[11]="2020-07-31,44.330002,44.419998,42.580002,44.360001,44.165276,1037800";
    Lines[12]="2020-08-03,44.560001,45.599998,43.419998,44.939999,44.742729,797000";
    Lines[13]="2020-08-04,44.900002,45.500000,43.450001,43.540001,43.348877,971100";
    Lines[14]="2020-08-05,44.860001,45.389999,43.650002,45.330002,45.131020,902000";
    Lines[15]="2020-08-06,45.049999,46.279999,44.330002,45.299999,45.101147,645200";
    Lines[16]="2020-08-07,44.849998,46.189999,44.189999,46.150002,45.947418,604900";
    Lines[17]="2020-08-10,46.669998,48.410000,46.549999,47.290001,47.082417,960200";
    Lines[18]="2020-08-11,49.110001,50.849998,48.799999,48.910000,48.695301,1187700";
    Lines[19]="2020-08-12,49.759998,50.009998,47.060001,47.840000,47.630001,752800";
    Lines[20]="2020-08-13,46.950001,48.369999,46.459999,47.110001,47.110001,535700";

    for (int i=1;i<Lines.length;i++)
    {
      Items=Lines[i].split(",");
      Date=Items[0].replace("-0","-");
      Price=Double.parseDouble(Items[5]);
      Volume=Long.parseLong(Items[6]);
      Items=Date.split("-");
      Year=Integer.parseInt(Items[0]);
      Month=Integer.parseInt(Items[1]);
      Day=Integer.parseInt(Items[2]);
      Price_series.add(new Day(Day,Month,Year),Price);
      Volume_Series.add(new Day(Day,Month,Year),Volume);
      Volume_Color_Vector.add(Volume>=Last_Volume?"+":"-");
      Last_Volume=Volume;
    }
  }

  @Override
  public void chartMouseClicked(ChartMouseEvent event)
  {
    // ignore
  }

  public void chartMouseMoved(ChartMouseEvent cmevent)
  {
    ChartEntity chartentity=cmevent.getEntity();
    if (chartentity instanceof XYItemEntity)
    {
      XYItemEntity e=(XYItemEntity)chartentity;
      XYDataset d=e.getDataset();
      int s=e.getSeriesIndex();
      int i=e.getItem();
      double x=d.getXValue(s,i);
      double y=d.getYValue(s,i);
      Out("x = "+x+"  y = "+y);
      xCrosshair.setValue(x);
      yCrosshair.setValue(y);
    }
  }

  String getYLabel(String Text)
  {
    String Result="";

    for (int i=0;i<Text.length();i++) Result+=Text.charAt(i)+(i<Text.length()-1?"\u2009":"");
//    Out(Result);
    return Result;
  }

  private static void out(String message) { System.out.print(message); }

  private static void Out(String message) { System.out.println(message); }

  // Create the GUI and show it. For thread safety, this method should be invoked from the event-dispatching thread.
  static void Create_And_Show_GUI()
  {
    final PriceVolume_Chart demo=new PriceVolume_Chart("ADS",19);

    JFrame frame=new JFrame("PriceVolume_Chart Frame");
    frame.add(demo);
    frame.addWindowListener(new WindowAdapter()
    {
      public void windowActivated(WindowEvent e) { }
      public void windowClosed(WindowEvent e) { }
      public void windowClosing(WindowEvent e) { System.exit(0); }
      public void windowDeactivated(WindowEvent e) { }
      public void windowDeiconified(WindowEvent e) { demo.repaint(); }
      public void windowGainedFocus(WindowEvent e) { demo.repaint(); }
      public void windowIconified(WindowEvent e) { }
      public void windowLostFocus(WindowEvent e) { }
      public void windowOpening(WindowEvent e) { demo.repaint(); }
      public void windowOpened(WindowEvent e) { }
      public void windowResized(WindowEvent e) { demo.repaint(); }
      public void windowStateChanged(WindowEvent e) { demo.repaint(); }
    });
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }

  public static void main(String[] args)
  {
    // Schedule a job for the event-dispatching thread : creating and showing this application's GUI.
    SwingUtilities.invokeLater(new Runnable() { public void run() { Create_And_Show_GUI(); } });
  }
}

class MyRender extends XYBarRenderer
{
  @Override
  public Paint getItemPaint(int row,int col)
  {
    this.setBarAlignmentFactor(0.5);
//    System.out.println(row+" "+col+" "+super.getItemPaint(row,col));
    return PriceVolume_Chart.Volume_Color_Vector.elementAt(col).equals("+")?super.getItemPaint(row,col):new Color(0.56f,0.2f,0.5f,1f);
  }
}



回答2:


Focusing narrowly on the question of "how to get the [x,y] values of a certain date," the NumberAxis methods java2DToValue() and valueToJava2D() illustrate the approach. CrosshairOverlayDemo1 is a concrete example, and the general principle is examined here.

Fortunately, you can highlight a chart element using just its data. In particular, the implementations of Annotation, Marker and Crosshair all work with data coordinates. As a concrete example, let PriceVolume_Chart implement ActionListener and add a javax.swing.Timer to the chart's constructor:

public PriceVolume_Chart(String Symbol) {
    …
    Timer t = new Timer(500, this);
    t.start();
}

Then, given a suitable index and listener, you'll see the crosshairs move to each date in succession at 2 Hz.

private int index;

@Override
public void actionPerformed(ActionEvent e) {
    TimeSeriesDataItem item = Volume_Series.getDataItem(index);
    xCrosshair.setValue(item.getPeriod().getFirstMillisecond());
    item = Price_series.getDataItem(index);
    yCrosshair.setValue(item.getValue().doubleValue());
    index++;
    if (index == Volume_Series.getItemCount()) {
        index = 0;
    }
}

You can use a similar listener to move your chosen indicator when the user selects a particular data entry. The exact details depend on your implementation of the observer pattern, discussed here. As you'll want to let both chart and table views share access to a common model, you may consider extending AbstractXYDataset, shown here and implementing a Swing TableModel; alternatively, consider extending AbstractTableModel, shown here and implementing the XYDataset interface.



来源：https://stackoverflow.com/questions/64201748/in-jfreechart-how-to-get-the-x-y-values-of-a-certain-point-on-the-chart

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