import java.awt.geom.*;
import java.awt.*;
class SpringView {
   private static final double xPoints[]={0,0.10, 0.125, 0.175, 0.225, 0.275, 0.325, 
                                          0.375, 0.425, 0.475, 0.525,0.575,0.625,
                                          0.675,0.725,0.775,0.825,0.875, 0.90,1.0};
   private static final double yPoints[]={0,0,-0.05,0.05,-0.05,0.05,-0.05,0.05,-0.05,0.05,
                                          -0.05,0.05,-0.05,0.05,-0.05,0.05,-0.05,0.05,0,0};
   private static final Path2D.Double polyline = 
                      new Path2D.Double(Path2D.WIND_EVEN_ODD,xPoints.length);
   private Stroke stroke;
   private Spring spring;

   static {  // static initialization block. It creates a spring of length = 1.
      polyline.moveTo (xPoints[0], yPoints[0]);
      for (int index = 1; index < xPoints.length;index++)
         polyline.lineTo(xPoints[index], yPoints[index]);
   }
   public SpringView(Spring spring) {
      this.spring = spring; 
      AffineTransform at = AffineTransform.getTranslateInstance(0,0);
      stroke = new BasicStroke(0.01f);
   }
   public Vector2D getAendPosition() {
      return spring.getAendPosition();
   }
   public Vector2D getBendPosition() {
      return spring.getBendPosition();
   }
   public void paint (Graphics2D g){
      Vector2D a=spring.getAendPosition();
      double restLength = spring.getRestLength();
      double ax = a.getX();
      double ay = a.getY();
      Vector2D v = spring.getBendPosition().minus(a);
      AffineTransform at = AffineTransform.getTranslateInstance(ax, ay);
      at.rotate(v.getX(), v.getY());
      at.scale(v.module(),  restLength);
      Path2D.Double shape = (Path2D.Double) at.createTransformedShape(polyline);
      if (v.module() < restLength)
         g.setColor(Color.BLACK);
      else
         g.setColor(Color.RED);
      g.setStroke(stroke);
      g.draw(shape);
   }
}