How To Draw Chart In Java

Just complementing Hovercraft Full Of Eels's solution:

I reworked his code, tweaked it a bit, adding a grid, axis labels and now the Y-axis goes from the minimum value present up to the maximum value. I planned on adding a couple of getters/setters but I didn't need them, you can add them if you want.

Here is the Gist link, I'll also paste the code below: GraphPanel on Gist

          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;  public class GraphPanel extends JPanel {      private int width = 800;     private int heigth = 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, heigth); //    }     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();          }       });    } }

It looks like this: Example pic