怎么在JPanel中实现用Jfreechar实现鼠标放上去就显示多条曲线交点上的数据

要在JPanel中使用JFreeChart实现鼠标放上去就显示多条曲线交点上的数据，需要对每条曲线都添加一个ChartMouseListener，并在mouseMoved()方法中计算出所有曲线的交点数据。

以下是示例代码：

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Line2D;
import java.util.ArrayList;
import java.util.List;
import org.jfree.chart.ChartMouseEvent;
import org.jfree.chart.ChartMouseListener;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.ValueAxis;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.XYItemRenderer;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYItemRendererState;
import org.jfree.data.xy.XYPointerAnnotation;
import org.jfree.ui.Layer;

public class MyChartPanel extends ChartPanel implements ChartMouseListener, MouseMotionListener {
    
    private List<Intersection> intersections = new ArrayList<>();
    private boolean showAnnotations = true;
    
    public MyChartPanel(JFreeChart chart) {
        super(chart);
        for (int i = 0; i < chart.getXYPlot().getDatasetCount(); i++) {
            chart.getXYPlot().getRenderer(i).addChangeListener(this);
            chart.getXYPlot().getRenderer(i).addChartMouseListener(this);
        }
        addMouseMotionListener(this);
    }
    
    @Override
    public void chartMouseClicked(ChartMouseEvent event) {
        // do nothing
    }

    @Override
    public void chartMouseMoved(ChartMouseEvent event) {
        intersections.clear();
        JFreeChart chart = event.getChart();
        XYPlot plot = chart.getXYPlot();
        double x = plot.getDomainAxis().java2DToValue(event.getTrigger().getX(), getScreenDataArea(), plot.getDomainAxisEdge());
        double y = plot.getRangeAxis().java2DToValue(event.getTrigger().getY(), getScreenDataArea(), plot.getRangeAxisEdge());
        for (int i = 0; i < plot.getDatasetCount(); i++) {
            XYDataset dataset = plot.getDataset(i);
            XYItemRenderer renderer = plot.getRenderer(i);
            ValueAxis domainAxis = plot.getDomainAxisForDataset(i);
            ValueAxis rangeAxis = plot.getRangeAxisForDataset(i);
            int seriesCount = dataset.getSeriesCount();
            for (int j = 0; j < seriesCount; j++) {
                int itemCount = dataset.getItemCount(j);
                for (int k = 0; k < itemCount - 1; k++) {
                    double x1 = dataset.getXValue(j, k);
                    double y1 = dataset.getYValue(j, k);
                    double x2 = dataset.getXValue(j, k + 1);
                    double y2 = dataset.getYValue(j, k + 1);
                    Intersection intersection = getIntersection(x, y, x1, y1, x2, y2, domainAxis, rangeAxis);
                    if (intersection != null) {
                        intersection.setSeriesIndex(j);
                        intersection.setItemIndex(k);
                        intersection.setRenderer(renderer);
                        intersections.add(intersection);
                    }
                }
            }
        }
        repaint();
    }
    
    private Intersection getIntersection(double x, double y, double x1, double y1, double x2, double y2, ValueAxis domainAxis, ValueAxis rangeAxis) {
        double dx = x2 - x1;
        double dy = y2 - y1;
        double dr2 = dx * dx + dy * dy;
        double D = x1 * y2 - x2 * y1;
        double discriminant = 5 * 5 * dr2 - D * D;
        if (discriminant < 0) {
            return null;
        }
        double sqrtDiscriminant = Math.sqrt(discriminant);
        double x3 = (D * dy + Math.signum(dy) * dx * sqrtDiscriminant) / dr2;
        double y3 = (-D * dx + Math.abs(dy) * sqrtDiscriminant) / dr2;
        double x4 = (D * dy - Math.signum(dy) * dx * sqrtDiscriminant) / dr2;
        double y4 = (-D * dx - Math.abs(dy) * sqrtDiscriminant) / dr2;
        if (Double.isNaN(x3) || Double.isNaN(y3) || Double.isNaN(x4) || Double.isNaN(y4)) {
            return null;
        }
        double xMin = Math.min(x1, x2);
        double xMax = Math.max(x1, x2);
        double yMin = Math.min(y1, y2);
        double yMax = Math.max(y1, y2);
        if (x3 < xMin || x3 > xMax || y3 < yMin || y3 > yMax || x4 < xMin || x4 > xMax || y4 < yMin || y4 > yMax) {
            return null;
        }
        double xValue = domainAxis.java2DToValue(x3, getScreenDataArea(), domainAxis.getEdge());
        double yValue = rangeAxis.java2DToValue(y3, getScreenDataArea(), rangeAxis.getEdge());
        return new Intersection(xValue, yValue, x3, y3, x4, y4);
    }
    
    public boolean isShowAnnotations() {
        return showAnnotations;
    }

    public void setShowAnnotations(boolean showAnnotations) {
        this.showAnnotations = showAnnotations;
        repaint();
    }
    
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (showAnnotations) {
            Graphics2D g2 = (Graphics2D) g;
            g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            for (Intersection intersection : intersections) {
                double x = intersection.getX();
                double y = intersection.getY();
                double x3 = intersection.getX3();
                double y3 = intersection.getY3();
                double x4 = intersection.getX4();
                double y4 = intersection.getY4();
                double dx = x4 - x3;
                double dy = y4 - y3;
                double angle = Math.atan2(dy, dx);
                double textX = x3 + 5 * Math.cos(angle);
                double textY = y3 + 5 * Math.sin(angle);
                XYPointerAnnotation annotation = new XYPointerAnnotation(String.format("(%.2f, %.2f)", x, y), x, y, angle);
                annotation.setBaseRadius(0);
                annotation.setTipRadius(5);
                annotation.setPaint(Color.black);
                intersection.setAnnotation(annotation);
                intersection.getRenderer().addAnnotation(annotation, Layer.FOREGROUND);
                g2.draw(new Line2D.Double(x3, y3, x4, y4));
            }
        }
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        // do nothing
    }

    @Override
    public void mouseMoved(MouseEvent e) {
        // do nothing
    }
    
    private static class Intersection {
        private double x;
        private double y;
        private double x3;
        private double y3;
        private double x4;
        private double y4;
        private int seriesIndex;
        private int itemIndex;
        private XYItemRenderer renderer;
        private XYPointerAnnotation annotation;
        
        public Intersection(double x, double y, double x3, double y3, double x4, double y4) {
            this.x = x;
            this.y = y;
            this.x3 = x3;
            this.y3 = y3;
            this.x4 = x4;
            this.y4 = y4;
        }

        public double getX() {
            return x;
        }

        public double getY() {
            return y;
        }

        public double getX3() {
            return x3;
        }

        public double getY3() {
            return y3;
        }

        public double getX4() {
            return x4;
        }

        public double getY4() {
            return y4;
        }

        public int getSeriesIndex() {
            return seriesIndex;
        }

        public void setSeriesIndex(int seriesIndex) {
            this.seriesIndex = seriesIndex;
        }

        public int getItemIndex() {
            return itemIndex;
        }

        public void setItemIndex(int itemIndex) {
            this.itemIndex = itemIndex;
        }

        public XYItemRenderer getRenderer() {
            return renderer;
        }

        public void setRenderer(XYItemRenderer renderer) {
            this.renderer = renderer;
        }

        public XYPointerAnnotation getAnnotation() {
            return annotation;
        }

        public void setAnnotation(XYPointerAnnotation annotation) {
            this.annotation = annotation;
        }
    }
}

在使用ChartPanel时，可以使用MyChartPanel代替原来的ChartPanel，并调用isShowAnnotations()和setShowAnnotations()方法来控制是否显示交点上的数据。注意，为了在交点上显示数据，需要在paintComponent()方法中添加XYPointerAnnotation，并将它们添加到XYItemRenderer中。同时，为了避免重复添加Annotation，需要在paintComponent()方法中先清除之前添加的Annotation。