// Learning Processing
  // Daniel Shiffman
  // http://www.learningprocessing.com
  
  // Example 22-2: Polymorphism
  
  class Shape {
    float x;
    float y;
    float r;
    
    Shape(float x_, float y_, float r_) {
      x = x_;
      y = y_;
      r = r_;
    }
    
    void jiggle() {
      x += random(-1,1);
      y += random(-1,1);
    }
    
    // A generic shape does not really know how to be displayed. 
    // This will be overridden in the child classes.
    void display() {
      point(x,y); 
    }
  }