Finding x and y values of a Line Chart

Question

Hi,
For instance, I had a line chart with x and y axis. When I move mouse to the line chart how can I determine x and y axis values? With mouseMoved metod i can find the coordinates but coordinates doesn't help me to find x and y values of the line chart.
How can I find x and y values of a Line Chart?
Thanks in advance

Answer 1

Translate from model to view and back. Another way to do this is to create an
AffineTransform for the modelToView and use it to transform the points. Create an inverse
transform to use in the viewToModel method. Add a ComponentListener and reset the transforms
in the componentResized method to keep them updated.
import java.awt.*;
import java.awt.event.*;
import java.awt.font.*;
import java.awt.geom.*;
import java.text.NumberFormat;
import javax.swing.*;
public class Translation extends JPanel {
    JLabel xLabel;
    JLabel yLabel;
    NumberFormat nf;
    double[] data = { 16.0, 32.9, 7.4, 18.9, 12.3 };
    final int Y_GRADS = 5;
    final int PAD = 35;
    final int SPAD = 3;
    final int TICK = 2;
    double maxVal;
    public Translation() {
        nf = NumberFormat.getInstance();
        nf.setMinimumFractionDigits(1);
        nf.setMaximumFractionDigits(1);
        maxVal = getMaxValue();
        addMouseMotionListener(sweep);
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        drawAxes(g2);
        plotData(g2);
    private void plotData(Graphics2D g2) {
        for(int j = 0; j < data.length; j++) {
            Point2D.Double p = modelToView(j, data[j]);
            if(j < data.length-1) {
                Point2D.Double next = modelToView(j+1, data[j+1]);
                g2.setPaint(Color.blue);
                g2.draw(new Line2D.Double(p, next));
            g2.setPaint(Color.red);
            g2.fill(new Ellipse2D.Double(p.x-2, p.y-2, 4, 4));
    private Point2D.Double modelToView(double x, double y) {
        double h = getHeight();
        Point2D.Double p = new Point2D.Double();
        p.x = PAD + x*(getWidth() - 2*PAD)/(data.length-1);
        p.y = h-PAD - y*(h - 2*PAD)/maxVal;
        return p;
    public Point2D.Double viewToModel(double x, double y) {
        double h = getHeight();
        Point2D.Double p = new Point2D.Double();
        p.x = (x - PAD) * (data.length-1) / (getWidth() - 2*PAD);
        p.y = (h - PAD - y) * maxVal / (h - 2*PAD);
        return p;
    private void drawAxes(Graphics2D g2) {
        int w = getWidth();
        int h = getHeight();
        double xInc = (double)(w - 2*PAD)/(data.length-1);
        double yInc = (double)(h - 2*PAD)/Y_GRADS;
        // Abcissa
        g2.draw(new Line2D.Double(PAD, h-PAD, w-PAD, h-PAD));
        // Tick marks
        double y1 = h-PAD, y2 = y1+TICK;
        for(int j = 0; j <= data.length; j++) {
            double x = PAD + j*xInc;
            g2.draw(new Line2D.Double(x, y1, x, y2));
        // Labels
        Font font = g2.getFont().deriveFont(14f);
        g2.setFont(font);
        FontRenderContext frc = g2.getFontRenderContext();
        LineMetrics lm = font.getLineMetrics("0", frc);
        float sx, sy = h - PAD + SPAD + lm.getAscent();
        for(int j = 0; j < data.length; j++) {
            String s = String.valueOf(j);
            float width = (float)font.getStringBounds(s, frc).getWidth();
            sx = (float)(PAD + j*xInc - width/2);
            g2.drawString(s, sx, sy);
        // Ordinate
        g2.draw(new Line2D.Double(PAD, PAD, PAD, h-PAD));
        // Tick marks
        double x1 = PAD, x2 = PAD-TICK;
        for(int j = 0; j <= Y_GRADS; j++) {
            double y = PAD + j*yInc;
            g2.draw(new Line2D.Double(x1, y, x2, y));
        // Labels
        for(int j = 0; j <= data.length; j++) {
            String s = nf.format(maxVal*(1.0 - (double)j/data.length));
            float width = (float)font.getStringBounds(s, frc).getWidth();
            sx = (float)(PAD - SPAD - width);
            sy = (float)(PAD + j*yInc + lm.getAscent()/3);
            g2.drawString(s, sx, sy);
    private double getMaxValue() {
        double max = -Double.MAX_VALUE;
        for(int j = 0; j < data.length; j++) {
            if(data[j] > max) {
                max = data[j];
        return max;
    MouseMotionListener sweep = new MouseMotionAdapter() {
        public void mouseMoved(MouseEvent e) {
            Point2D.Double p = viewToModel(e.getX(), e.getY());
            xLabel.setText(nf.format(p.x));
            yLabel.setText(nf.format(p.y));
    private JPanel getLast() {
        xLabel = new JLabel();
        yLabel = new JLabel();
        Dimension d = new Dimension(45, 25);
        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.insets = new Insets(2,2,2,2);
        addComponents(new JLabel("x ="), xLabel, panel, gbc, d, true);
        addComponents(new JLabel("y ="), yLabel, panel, gbc, d, false);
        return panel;
    private void addComponents(JComponent c1, JComponent c2, Container c,
                               GridBagConstraints gbc, Dimension d, boolean b) {
        gbc.weightx = b ? 1.0 : 0;
        gbc.anchor = GridBagConstraints.EAST;
        c.add(c1, gbc);
        c2.setPreferredSize(d);
        gbc.weightx = b ? 0 : 1.0;
        gbc.anchor = GridBagConstraints.WEST;
        c.add(c2, gbc);
    public static void main(String[] args) {
        Translation test = new Translation();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(test);
        f.getContentPane().add(test.getLast(), "Last");
        f.setSize(500,400);
        f.setLocation(200,200);
        f.setVisible(true);
}