import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.HeadlessException;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;


public class Rectangles extends JFrame {

    private int rectangles=1;
    private Random random = new Random();

    public Rectangles() {
        super();
        setLayout(new BorderLayout());
        JButton more = new JButton("more");
        JButton fewer = new JButton("fewer");
        more.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                rectangles*=2;
                Rectangles.this.repaint();
            }
        });
        fewer.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                if(rectangles>=2){
                    rectangles/=2;
                    Rectangles.this.repaint();
                }
            }
        });
        JPanel panel = new JPanel(){

            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.BLACK);
                for(int i=1;i<=rectangles;i++){
                    int x= (int)Math.round(random.nextDouble()*getWidth());
                    int y=(int)Math.round(random.nextDouble()*getHeight());
                    int w = (int)Math.round(random.nextDouble()*(getWidth()-x));
                    int h = (int)Math.round(random.nextDouble()*(getHeight()-y));
                    g.drawRect(x, y, w, h);
                }
            }

        };
        add(more,BorderLayout.EAST);
        add(fewer,BorderLayout.WEST);
        add(panel,BorderLayout.CENTER);
    }

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

            @Override
            public void run() {
                Rectangles r = new Rectangles();
                r.setTitle("Random rectangles demo");
                r.setSize(new Dimension(400,300));
                r.setVisible(true);
            }

        });

    }

}