// The colored box is a subclassof box...
 class coloredBox extends box { 

 // new attribute
   color boxColor;

 // new constructor
   coloredBox(float _x, float _y, float _w, float _h, int _n, color _c) {
   super(_x, _y, _w, _h, _n);
   boxColor = _c;
   } // coloredBox

 void display() {
   pushMatrix();
   // draw the box
   translate(x, y);
   stroke(0);
   fill(boxColor);
   rect(0, 0, w, h);
   // draw the balls in it
   for (int i=0; i < balls.length; i++) {
   balls[i].display();
   }
   popMatrix();
   } // display()
   } // class coloredBox