Drawing a GUI Multiplication Table

/*
 * Write a program that displays a multiplication table in a panel using the drawing methods, as shown in Figure 13.27a.
 */

import java.awt.*;
import javax.swing.*;

@SuppressWarnings("serial")
public class DisplayAMultiplicationTable extends JFrame
{
    // Constructor
    public DisplayAMultiplicationTable()
    {
        add(new MultiplicationTablePanel());
    }

    // Main method
    public static void main(String[] args)
    {
        DisplayAMultiplicationTable frame = new DisplayAMultiplicationTable();
        frame.setSize(300, 400);
        frame.setTitle("Exercise 13_04");
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

@SuppressWarnings("serial")
// New class
class MultiplicationTablePanel extends JPanel
{
    @Override
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);

        // Declaration
        int x = 10, y = 40, i = 0; // x & y = start point for "paint brush"
        String s = "";

        // Display the title
        g.setColor(Color.RED);
        g.setFont(new Font("Times", Font.BOLD, 20));
        g.drawString("Multiplication Table", x + 50, y);

        // Font for numbers
        g.setFont(new Font("Times", Font.BOLD, 15));

        y += 30; // Move down 30 pixels
        for(i = 1; i < 10; i++) // Vertical row
            g.drawString("   " + i, x + 10, y + 10 + i * 20); // Spaces move line left/right, prints downwards

        x += 40; // Move right 40 pixels
        for(i = 1; i < 10; i++)
        {
            s = s + "   " + i; // Create full string
        }
        g.drawString(s, x, y); // Then print horizontally (top)

        y += 10;
        g.drawRect(x, y, 200, 200); // Draw border

        s = ""; // Reset string
        y += 20; // Move down 20
        // x does not need to be reset string will add spaces after last printed vertical numbers

        for(i = 1; i < 10; i++)
        {
            for(int j = 1; j < 10; j++)
            {
                if(i * j < 10)
                    s = s + "   " + i * j; // Builds entire row with spaces
                else
                    s = s + " " + i * j; // Accounts for single and double digits
            }

            g.drawString(s, x, y); // Print built string
            s = ""; // Reset string
            y += 20; // Move down one row
        }
    }
}