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

    public class SwingMain extends JPanel implements MouseListener {

        final static int SEPARATION = 125;
        final static int DIAMETER = 15;
        final static int NBALLS = 5;
        final static int WIDTH = (NBALLS + 1) * (SEPARATION + DIAMETER);
        final static int HEIGHT = (NBALLS + 1) * (SEPARATION);
        final static int XSTART = SEPARATION;
        final static int YSTART = SEPARATION;
        JFrame frame = new JFrame();

        public static void main(String[] args) {
            SwingUtilities.invokeLater(() -> new SwingMain().start());
        }

        public void start() {
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            setPreferredSize(new Dimension(WIDTH, HEIGHT));
            frame.add(this);
            setBackground(Color.gray);
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g;

            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            g2d.setColor(Color.white);

            int y = YSTART;
            for (int r = 0; r < NBALLS; r++) {
                int x = XSTART;
                for (int c = 0; c < NBALLS; c++) {
                    g2d.fillOval(x, y, DIAMETER, DIAMETER);
                    x += SEPARATION;
                }
                y += SEPARATION;
            }

            drawHorizontalLine(g2d, 0, 0);
            drawButton(g2d);
        }

        public void drawHorizontalLine(Graphics2D g, int r, int c) {
            int x1 = (SEPARATION) * (c + 1);
            int x2 = x1 + SEPARATION;
            int y1 = (SEPARATION) * (r + 1) + 2;
            int y2 = SEPARATION * (r + 1) + 6;
            drawRectangle(g, x1, y1, x2, y2, Color.WHITE);
        }

        public void drawRectangle(Graphics2D graphic, int x1, int y1, int x2, int y2, Color c) {
            graphic.fillRect(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x1 - x2), Math.abs(y1 - y2));
        }

        private void drawButton(Graphics2D g) {
            int centerX = WIDTH / 2;
            int x1 = centerX - 100;
            int x2 = centerX + 100;
            int y1 = 25;
            int y2 = 75;
            drawRectangle(g, x1, y1, x2, y2, Color.WHITE);
            FontMetrics fm = g.getFontMetrics();
            g.setColor(Color.gray);
            g.setFont(new Font("TimesRoman", Font.BOLD, 20));
            int strWidth = fm.stringWidth("Completed.");
            int strHeight = fm.getAscent();
            g.drawString("Completed.",
                      (centerX - 20) - strWidth / 2,
                      45 + strHeight);
        }

        public void mousePressed(MouseEvent e) {
            //If the area of the button is clicked
            System.out.println("Button clicked.");
        }
        public void mouseClicked(MouseEvent e) {}
        public void mouseReleased(MouseEvent e) {}
        public void mouseEntered(MouseEvent e) {}
        public void mouseExited(MouseEvent e) {}

    }