A simple Swing component to draw a Graph over a regular JPanel. Features a grid, customizable amount of hatch marks, axis labels,checking for minimum and maximum value to label correctly the Y-axis and customizable padding and label padding. Based on "Hovercraft Full Of Eels"'s answer on StackOverflow (http://stackoverflow.com/questions/8693342/…

GraphPanel.java

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.Stroke;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

/**
 *
 * @author "Hovercraft Full of Eels", "Rodrigo Azevedo"
 *
 * This is an improved version of Hovercraft Full of Eels (https://stackoverflow.com/users/522444/hovercraft-full-of-eels)
 * answer on StackOverflow: https://stackoverflow.com/a/8693635/753012
 *
 * GitHub user @maritaria has made some performance improvements which can be found in the comment section of this Gist.
 */
public class GraphPanel extends JPanel {
    private int width = 800;
    private int height = 400;
    private int padding = 25;
    private int labelPadding = 25;
    private Color lineColor = new Color(44, 102, 230, 180);
    private Color pointColor = new Color(100, 100, 100, 180);
    private Color gridColor = new Color(200, 200, 200, 200);
    private static final Stroke GRAPH_STROKE = new BasicStroke(2f);
    private int pointWidth = 4;
    private int numberYDivisions = 10;
    private List<Double> scores;

    public GraphPanel(List<Double> scores) {
        this.scores = scores;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

        double xScale = ((double) getWidth() - (2 * padding) - labelPadding) / (scores.size() - 1);
        double yScale = ((double) getHeight() - 2 * padding - labelPadding) / (getMaxScore() - getMinScore());

        List<Point> graphPoints = new ArrayList<>();
        for (int i = 0; i < scores.size(); i++) {
            int x1 = (int) (i * xScale + padding + labelPadding);
            int y1 = (int) ((getMaxScore() - scores.get(i)) * yScale + padding);
            graphPoints.add(new Point(x1, y1));
        }

        // draw white background
        g2.setColor(Color.WHITE);
        g2.fillRect(padding + labelPadding, padding, getWidth() - (2 * padding) - labelPadding, getHeight() - 2 * padding - labelPadding);
        g2.setColor(Color.BLACK);

        // create hatch marks and grid lines for y axis.
        for (int i = 0; i < numberYDivisions + 1; i++) {
            int x0 = padding + labelPadding;
            int x1 = pointWidth + padding + labelPadding;
            int y0 = getHeight() - ((i * (getHeight() - padding * 2 - labelPadding)) / numberYDivisions + padding + labelPadding);
            int y1 = y0;
            if (scores.size() > 0) {
                g2.setColor(gridColor);
                g2.drawLine(padding + labelPadding + 1 + pointWidth, y0, getWidth() - padding, y1);
                g2.setColor(Color.BLACK);
                String yLabel = ((int) ((getMinScore() + (getMaxScore() - getMinScore()) * ((i * 1.0) / numberYDivisions)) * 100)) / 100.0 + "";
                FontMetrics metrics = g2.getFontMetrics();
                int labelWidth = metrics.stringWidth(yLabel);
                g2.drawString(yLabel, x0 - labelWidth - 5, y0 + (metrics.getHeight() / 2) - 3);
            }
            g2.drawLine(x0, y0, x1, y1);
        }

        // and for x axis
        for (int i = 0; i < scores.size(); i++) {
            if (scores.size() > 1) {
                int x0 = i * (getWidth() - padding * 2 - labelPadding) / (scores.size() - 1) + padding + labelPadding;
                int x1 = x0;
                int y0 = getHeight() - padding - labelPadding;
                int y1 = y0 - pointWidth;
                if ((i % ((int) ((scores.size() / 20.0)) + 1)) == 0) {
                    g2.setColor(gridColor);
                    g2.drawLine(x0, getHeight() - padding - labelPadding - 1 - pointWidth, x1, padding);
                    g2.setColor(Color.BLACK);
                    String xLabel = i + "";
                    FontMetrics metrics = g2.getFontMetrics();
                    int labelWidth = metrics.stringWidth(xLabel);
                    g2.drawString(xLabel, x0 - labelWidth / 2, y0 + metrics.getHeight() + 3);
                }
                g2.drawLine(x0, y0, x1, y1);
            }
        }

        // create x and y axes 
        g2.drawLine(padding + labelPadding, getHeight() - padding - labelPadding, padding + labelPadding, padding);
        g2.drawLine(padding + labelPadding, getHeight() - padding - labelPadding, getWidth() - padding, getHeight() - padding - labelPadding);

        Stroke oldStroke = g2.getStroke();
        g2.setColor(lineColor);
        g2.setStroke(GRAPH_STROKE);
        for (int i = 0; i < graphPoints.size() - 1; i++) {
            int x1 = graphPoints.get(i).x;
            int y1 = graphPoints.get(i).y;
            int x2 = graphPoints.get(i + 1).x;
            int y2 = graphPoints.get(i + 1).y;
            g2.drawLine(x1, y1, x2, y2);
        }

        g2.setStroke(oldStroke);
        g2.setColor(pointColor);
        for (int i = 0; i < graphPoints.size(); i++) {
            int x = graphPoints.get(i).x - pointWidth / 2;
            int y = graphPoints.get(i).y - pointWidth / 2;
            int ovalW = pointWidth;
            int ovalH = pointWidth;
            g2.fillOval(x, y, ovalW, ovalH);
        }
    }

//    @Override
//    public Dimension getPreferredSize() {
//        return new Dimension(width, height);
//    }

    private double getMinScore() {
        double minScore = Double.MAX_VALUE;
        for (Double score : scores) {
            minScore = Math.min(minScore, score);
        }
        return minScore;
    }

    private double getMaxScore() {
        double maxScore = Double.MIN_VALUE;
        for (Double score : scores) {
            maxScore = Math.max(maxScore, score);
        }
        return maxScore;
    }

    public void setScores(List<Double> scores) {
        this.scores = scores;
        invalidate();
        this.repaint();
    }

    public List<Double> getScores() {
        return scores;
    }
    
    private static void createAndShowGui() {
        List<Double> scores = new ArrayList<>();
        Random random = new Random();
        int maxDataPoints = 40;
        int maxScore = 10;
        for (int i = 0; i < maxDataPoints; i++) {
            scores.add((double) random.nextDouble() * maxScore);
//            scores.add((double) i);
        }
        GraphPanel mainPanel = new GraphPanel(scores);
        mainPanel.setPreferredSize(new Dimension(800, 600));
        JFrame frame = new JFrame("DrawGraph");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
    
    public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

Hey there, I really like this code and I wanted to ask, what is the license on this code? Am I allowed to use it?

Does this code have a license?

No License?

This code is a transformation of code that was posted on StackOverflow which marks user contributions licensed under cc by-sa 3.0 with attribution required.

Hey, in next revision you can fix typos at lines.
28. private int heigth = 400;
130. // return new Dimension(width, heigth);

I wanna draw this simple line with these two points P 1 ={ 5, 8} points P 2 = { 12 , 18 } how to change the random to this point??

There are some optimizations you can do with this code to improve performance, such as caching the values for the getMinScore and getMaxScore functions as the paintComponent calls these many times during various for loops. The implementation of these functions have complexity of n (being the number of scores in the graph), since the for loops have the same complexity this means you are executing these n times as well, making the paint operation n^2, while it could be n when using caching. Note that you still have to iterate the list of values multiple times, but at least the complexity increases linear instead of quadratic.

I refactored it a bit, applied the optimization I mentioned. Also I added in to skip drawing the dots if they will be indistinguishable on the screen. For my project I was using integers so the data is now integers as well as the labels, but you can put back the original label code if you need that.

import javax.swing.*;
import java.awt.*;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

/**
 * @author Rodrigo, Maritaria
 */
public final class GraphView extends JPanel {
    private final static int padding = 25;
    private final static int labelPadding = 25;
    private final static int pointWidth = 4;
    private final static int numberYDivisions = 10;
    private final static Color lineColor = new Color(44, 102, 230, 180);
    private final static Color pointColor = new Color(100, 100, 100, 180);
    private final static Color gridColor = new Color(200, 200, 200, 200);
    private static final Stroke graphStroke = new BasicStroke(2f);
    private List<Integer> values = new ArrayList<>(10);

    public GraphView() {
        setPreferredSize(new Dimension(padding * 2 + 300, padding * 2 + 200));
    }

    public void setValues(Collection<Integer> newValues) {
        values.clear();
        addValues(newValues);
    }

    public void addValues(Collection<Integer> newValues) {
        values.addAll(newValues);
        updateUI();
    }

    @Override
    protected void paintComponent(Graphics graphics) {
        super.paintComponent(graphics);
        if (!(graphics instanceof Graphics2D)) {
            graphics.drawString("Graphics is not Graphics2D, unable to render", 0, 0);
            return;
        }
        final Graphics2D g = (Graphics2D) graphics;
        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

        final var length = values.size();
        final var width = getWidth();
        final var height = getHeight();
        final var maxScore = getMaxScore();
        final var minScore = getMinScore();
        final var scoreRange = maxScore - minScore;

        // draw white background
        g.setColor(Color.WHITE);
        g.fillRect(
                padding + labelPadding,
                padding,
                width - (2 * padding) - labelPadding,
                height - 2 * padding - labelPadding);
        g.setColor(Color.BLACK);

        final FontMetrics fontMetrics = g.getFontMetrics();
        final int fontHeight = fontMetrics.getHeight();

        // create hatch marks and grid lines for y axis.
        for (int i = 0; i < numberYDivisions + 1; i++) {
            final int x1 = padding + labelPadding;
            final int x2 = pointWidth + padding + labelPadding;
            final int y = height - ((i * (height - padding * 2 - labelPadding)) / numberYDivisions + padding + labelPadding);
            if (length > 0) {
                g.setColor(gridColor);
                g.drawLine(padding + labelPadding + 1 + pointWidth, y, width - padding, y);
                g.setColor(Color.BLACK);
                final int tickValue = (int) (minScore + ((scoreRange * i) / numberYDivisions));
                final String yLabel = tickValue + "";
                final int labelWidth = fontMetrics.stringWidth(yLabel);
                g.drawString(yLabel, x1 - labelWidth - 5, y + (fontHeight / 2) - 3);
            }
            g.drawLine(x1, y, x2, y);
        }

        // and for x axis
        if (length > 1) {
            for (int i = 0; i < length; i++) {
                final int x = i * (width - padding * 2 - labelPadding) / (length - 1) + padding + labelPadding;
                final int y1 = height - padding - labelPadding;
                final int y2 = y1 - pointWidth;
                if ((i % ((int) ((length / 20.0)) + 1)) == 0) {
                    g.setColor(gridColor);
                    g.drawLine(x, height - padding - labelPadding - 1 - pointWidth, x, padding);
                    g.setColor(Color.BLACK);
                    final String xLabel = i + "";
                    final int labelWidth = fontMetrics.stringWidth(xLabel);
                    g.drawString(xLabel, x - labelWidth / 2, y1 + fontHeight + 3);
                }
                g.drawLine(x, y1, x, y2);
            }
        }

        // create x and y axes 
        g.drawLine(padding + labelPadding, height - padding - labelPadding, padding + labelPadding, padding);
        g.drawLine(
                padding + labelPadding,
                height - padding - labelPadding,
                width - padding,
                height - padding - labelPadding);

        final Stroke oldStroke = g.getStroke();
        g.setColor(lineColor);
        g.setStroke(graphStroke);

        final double xScale = ((double) width - (2 * padding) - labelPadding) / (length - 1);
        final double yScale = ((double) height - 2 * padding - labelPadding) / scoreRange;

        final List<Point> graphPoints = new ArrayList<>(length);
        for (int i = 0; i < length; i++) {
            final int x1 = (int) (i * xScale + padding + labelPadding);
            final int y1 = (int) ((maxScore - values.get(i)) * yScale + padding);
            graphPoints.add(new Point(x1, y1));
        }

        for (int i = 0; i < graphPoints.size() - 1; i++) {
            final int x1 = graphPoints.get(i).x;
            final int y1 = graphPoints.get(i).y;
            final int x2 = graphPoints.get(i + 1).x;
            final int y2 = graphPoints.get(i + 1).y;
            g.drawLine(x1, y1, x2, y2);
        }

        boolean drawDots = width > (length * pointWidth);
        if (drawDots) {
            g.setStroke(oldStroke);
            g.setColor(pointColor);
            for (Point graphPoint : graphPoints) {
                final int x = graphPoint.x - pointWidth / 2;
                final int y = graphPoint.y - pointWidth / 2;
                g.fillOval(x, y, pointWidth, pointWidth);
            }
        }
    }

    private double getMinScore() {
        return values.stream().min(Integer::compareTo).orElse(0);
    }

    private double getMaxScore() {
        return values.stream().max(Integer::compareTo).orElse(0);
    }
}

@maritaria Thanks you for the optimization! I did this for a university assignment and never looked back at it, didn't even notice people asking about the license (sorry everyone). I will point to your version instead of just copying it into my gist.

@ashishrana160796 typos fixed :)