import java.awt.*;
import java.awt.event.*;
import java.applet.*;

public class Henon extends Applet implements ActionListener
{
   private double xmin = -2, xmax = 2, ymin = -2, ymax = 2;
   private double a = 1.4, b = -0.3, x = 0, y = 0;

   private Button start = new Button("Start");
   private TextField inputA = new TextField("1.400");
   private TextField inputB = new TextField("-0.30");
   private TextField inputX = new TextField("0.000");
   private TextField inputY = new TextField("0.000");
   private boolean draw = false;

   public void init()
   {  Panel input = new Panel();
      input.setLayout(new FlowLayout());
      input.add(new Label("a: "));
      input.add(inputA);
      input.add(new Label("b: "));
      input.add(inputB);
      input.add(new Label("X0: "));
      input.add(inputX);
      input.add(new Label("Y0: "));
      input.add(inputY);
      input.add(start);
      start.addActionListener(this);

      setLayout(new BorderLayout());
      add("South", input);
   }
   public void paint(Graphics g)
   {
      g.drawRect(0,0, getSize().width-1, getSize().height-1);
      if (draw)
      {
         double xx = 0;
         for (int i = 0; i < 5000; i++)
         {
            xx = x;
            x = a - b*y - x*x;
            y = xx;
         }

         for (int i = 0; i < 50000; i++)
         {
            xx = x;
            x = a - b*y - x*x;
            y = xx;
            int ix = toScreen(x, getSize().width, xmin, xmax);
            int iy = toScreen(y, getSize().height, ymax, ymin);
            g.fillRect(ix, iy, 2, 2);
         }
      }
   }

   public void actionPerformed(ActionEvent ae)
   {  if (ae.getSource() == start)
      {
         a = toDouble(inputA.getText());
         b = toDouble(inputB.getText());
         x = toDouble(inputX.getText());
         y = toDouble(inputY.getText());
         draw = true;
         repaint();
      }
   }

   public int toScreen(double x, int iMax, double min, double max)
   {
      return (int)Math.round( iMax / (max - min) * (x - max) + iMax);
   }

   public double toDouble(String x)
   {
      try
      {
         Double num = new Double(x);
         return num.doubleValue();
      }
      catch(Exception ie)
      {  return 0.0; }
   }
}