labeling for graph in java swing

Question

This drawing a simple line graph in Java stack-overflow stuffs gives a good idea for drawing a line graph..but i'm not getting how to label the X and Y-axis within the graph. Can anyone please tell me how to label the x and y coordinates.

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
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.*;

@SuppressWarnings("serial")
public class DrawGraph extends JPanel {
   private static final int MAX_SCORE = 20;
   private static final int PREF_W = 800;
   private static final int PREF_H = 650;
   private static final int BORDER_GAP = 30;
   private static final Color GRAPH_COLOR = Color.green;
   private static final Color GRAPH_POINT_COLOR = new Color(150, 50, 50, 180);
   private static final Stroke GRAPH_STROKE = new BasicStroke(3f);
   private static final int GRAPH_POINT_WIDTH = 12;
   private static final int Y_HATCH_CNT = 10;
   private List<Integer> scores;

   public DrawGraph(List<Integer> 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 * BORDER_GAP) / (scores.size() - 1);
      double yScale = ((double) getHeight() - 2 * BORDER_GAP) / (MAX_SCORE - 1);

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

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

      // create hatch marks for y axis. 
      for (int i = 0; i < Y_HATCH_CNT; i++) {
         int x0 = BORDER_GAP;
         int x1 = GRAPH_POINT_WIDTH + BORDER_GAP;
         int y0 = getHeight() - (((i + 1) * (getHeight() - BORDER_GAP * 2)) / Y_HATCH_CNT + BORDER_GAP);
         int y1 = y0;
         g2.drawLine(x0, y0, x1, y1);
      }

      // and for x axis
      for (int i = 0; i < scores.size() - 1; i++) {
         int x0 = (i + 1) * (getWidth() - BORDER_GAP * 2) / (scores.size() - 1) + BORDER_GAP;
         int x1 = x0;
         int y0 = getHeight() - BORDER_GAP;
         int y1 = y0 - GRAPH_POINT_WIDTH;
         g2.drawLine(x0, y0, x1, y1);
      }

      Stroke oldStroke = g2.getStroke();
      g2.setColor(GRAPH_COLOR);
      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(GRAPH_POINT_COLOR);
      for (int i = 0; i < graphPoints.size(); i++) {
         int x = graphPoints.get(i).x - GRAPH_POINT_WIDTH / 2;
         int y = graphPoints.get(i).y - GRAPH_POINT_WIDTH / 2;;
         int ovalW = GRAPH_POINT_WIDTH;
         int ovalH = GRAPH_POINT_WIDTH;
         g2.fillOval(x, y, ovalW, ovalH);
      }
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   private static void createAndShowGui() {
      List<Integer> scores = new ArrayList<Integer>();
      Random random = new Random();
      int maxDataPoints = 16;
      int maxScore = 20;
      for (int i = 0; i < maxDataPoints ; i++) {
         scores.add(random.nextInt(maxScore));
      }
      DrawGraph mainPanel = new DrawGraph(scores);

      JFrame frame = new JFrame("DrawGraph");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

Answer 1

A lot will come down to "where" you want to render the text.

What I means is, do you want to modify the position of the existing lines, or do you want to render with the BORDER_GAP

You can start by having a look at Working with Text APIs

You could start with something simple, such as...

FontMetrics fm = g2.getFontMetrics();
// create hatch marks for y axis. 
for (int i = 0; i < Y_HATCH_CNT; i++) {
    int x0 = BORDER_GAP;
    int x1 = GRAPH_POINT_WIDTH + BORDER_GAP;
    int y0 = getHeight() - (((i + 1) * (getHeight() - BORDER_GAP * 2)) / Y_HATCH_CNT + BORDER_GAP);
    int y1 = y0;
    g2.drawLine(x0, y0, x1, y1);
    String value = Integer.toString(i);
    g2.drawString(value, x0 - fm.stringWidth(value), y0 + (fm.getAscent() / 2));
}

// and for x axis
for (int i = 0; i < scores.size() - 1; i++) {
    int x0 = (i + 1) * (getWidth() - BORDER_GAP * 2) / (scores.size() - 1) + BORDER_GAP;
    int x1 = x0;
    int y0 = getHeight() - BORDER_GAP;
    int y1 = y0 - GRAPH_POINT_WIDTH;
    g2.drawLine(x0, y0, x1, y1);
    String value = Integer.toString(i);
    g2.drawString(value, x0 - (fm.stringWidth(value) / 2), y0 + fm.getAscent());
}

Which will renderer a number (corresponding to the index of the loop) next to each hatch for example...

Updated with rotation example

Now if you wanted to rotate, say the x-series, so the labels ran vertically, you could do something like...

FontMetrics fm = g2.getFontMetrics();
// create hatch marks for y axis. 
for (int i = 0; i < Y_HATCH_CNT; i++) {
    int x0 = BORDER_GAP;
    int x1 = GRAPH_POINT_WIDTH + BORDER_GAP;
    int y0 = getHeight() - (((i + 1) * (getHeight() - BORDER_GAP * 2)) / Y_HATCH_CNT + BORDER_GAP);
    int y1 = y0;
    g2.drawLine(x0, y0, x1, y1);
    AffineTransform oldTransform = g2.getTransform();
    AffineTransform newTransform = new AffineTransform();
    newTransform.translate(-fm.getHeight() / 2, 0);
    newTransform.rotate(Math.toRadians(-90), x0, y0);
    g2.setTransform(newTransform);
    String value = Integer.toString(i);
    g2.drawString(value, x0 - (fm.stringWidth(value) / 2), y0 + (fm.getAscent() / 2));
    g2.setTransform(oldTransform);
}