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

public class PiToothpicks extends JApplet implements ActionListener {
    
    private JLabel linesLabel, toothpickLabel;
    private JTextField linesField, toothpickField;
    private JButton againButton;

    public void init() {

      Container container = getContentPane();  
      container.setLayout( new FlowLayout() ); 

      linesLabel = new JLabel( "Number of grid lines" );
      linesField = new JTextField( "10", 4 );
      container.add( linesLabel );
      container.add( linesField );
      linesField.addActionListener( this );

      toothpickLabel = new JLabel( "Number of toothpicks to drop randomly" );
      toothpickField = new JTextField( "100", 4 );
      container.add( toothpickLabel );
      container.add( toothpickField );
      toothpickField.addActionListener( this );

      againButton = new JButton( "Again!" );
      container.add( againButton );

      againButton.addActionListener( this );


    }


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


    public void paint( Graphics g )
    {
       super.paint( g );

       int x1, y1, x2, y2;
       double angle;
       int xcenter, ycenter;
       int toothpicks;
       int gridlines;
       int length;
       int[] y;
       int k;
       double distanceToLine;
       int M=0;
       double projectionLength;

       gridlines = Integer.parseInt(linesField.getText());
       y = new int[gridlines+1];
       length = getHeight() / gridlines;
       g.setColor( Color.CYAN);
       for (int i=1; i<=gridlines; i++) {
	   y[i] = getHeight()/gridlines*i;
	   g.drawLine(0,y[i],getWidth(),y[i]);
       }
       toothpicks = Integer.parseInt(toothpickField.getText());

       g.setColor(Color.BLACK);

       for (int i=1; i<=toothpicks; i++) {
	   x1 = (int)(Math.random() * getWidth());
	   y1 = (int)(Math.random() * getHeight());
	   angle = Math.random() * 2 * Math.PI;    //radians
	   x2 = (int)(Math.cos(angle) * length + x1);
	   y2 = (int)(Math.sin(angle) * length + y1);

 	   ycenter = (y1 + y2) / 2;
	   //find closest line
	   k = 0;
	   distanceToLine = ycenter;
	   //find nearest grid line to this line's y center.
	   while (k<=gridlines && Math.abs(ycenter - y[k]) <= distanceToLine) 
	       distanceToLine = Math.abs(ycenter - y[k++]);
	   //projectionLength = Math.sin(angle) * length;
	   projectionLength = Math.abs(Math.sin(angle) * 0.5 * length);
	   if (projectionLength > distanceToLine) {
	       M++;
	       g.setColor(Color.RED);
	   }
	   else 
	       g.setColor(Color.BLACK);

	   g.drawLine(x1,y1,x2,y2);
       }
       
       showStatus("2 * #toothpicks / #intersections = " + 2.0*toothpicks/M +
		  "  M=" + M);
   }
}