/****************************************************************************
** COPYRIGHT (C):    1997 Cay S. Horstmann. All Rights Reserved.
** PROJECT:          Practical OO Development with C++ and Java
** FILE:             CloudApplet.java
** PURPOSE:          to show that Applet is a framework (ch. 19)
** VERSION           1.0
** PROGRAMMERS:      Cay Horstmann (CSH)
** RELEASE DATE:     3-15-97 (CSH)
** UPDATE HISTORY:
****************************************************************************/

import java.applet.*;
import java.awt.*;
import java.util.*;

public class CloudApplet extends Applet
{  public boolean mouseDown(Event evt, int x, int y)
   {  _points.addElement(new Point(x, y));
      repaint();
      return true;
   }

   public void paint(Graphics g)
   {  for (int i = 0; i < _points.size(); i++)
      {  Point p = (Point)_points.elementAt(i);
         g.drawOval(p.x - 2, p.y - 2, 5, 5);
      }
      if (regression())
      {  int xright = size().width;
         g.drawLine(0, (int)b, xright, (int) (m * xright + b));
      }
   }

   private boolean regression()
   {  double sx = 0;
      double sxx = 0;
      double sy = 0;
      double sxy = 0;
      int n = _points.size();
      if (n < 2) return false;
      for (int i = 0; i < n; i++)
      {  Point p = (Point)_points.elementAt(i);
         int x = p.x;
         int y = p.y;
         sx += x;
         sy += y;
         sxx += x * x;
         sxy += x * y;
      }
      double den = sxx - sx * sx / n;
      if (den == 0) return false;
      m = (sxy - sx * sy / n) / den;
      b = (sy - m * sx) / n;
      return true;
   }


   private Vector _points = new Vector();
   private double m;
   private double b;
}