import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.event.ActionListener; 
import java.awt.event.ActionEvent; 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class PiEstimate extends JPanel implements ActionListener
{
    private int tries, hits;
    public static final int SIZE = 400;

    public PiEstimate() {
        tries = 0;
        hits = 0; 
        Timer clock = new Timer(10, this); 
        clock.start();
    }

    public void paintComponent(Graphics g) {
        int x = (int)(SIZE*Math.random() ); 
        int y = (int)(SIZE*Math.random() ); 
        tries++;
        int r = SIZE/2;
        g.setColor(Color.BLACK);
        g.drawOval(0,0, SIZE, SIZE); 
        g.drawString( "Hits: "+ hits + "  Tries: " + tries, r/2, r);
        double pi = 4.0* (double)hits/(double)(tries);
        g.drawString( "PI is about: "+ pi , r/2, r+20);

        if( (x-r)*(x-r) + (y-r)*(y-r) <= r*r)
        {
            hits++;
            g.setColor(Color.RED);
        }
        g.fillOval(x,y, 10, 10 );
    }

    public void actionPerformed(ActionEvent e) {
        repaint(); 
    }

    public static void main(String args) {
        JFrame w = new JFrame("Estimate Pi"); 
        w.setSize(SIZE, SIZE+20);
        Container c = w.getContentPane(); 
        c.add(new PiEstimate());
        w.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        w.setResizable(false);
        w.setVisible(true);
    } 

}