Bubble class Processing

class Bubble{
  int diameter, x, y;

  Bubble(int d){
     diameter = d;
     x = (int)(Math.random() * width);
     y = (int)(Math.random() * height);
  }

  void display(){
    ellipse(x, y, diameter, diameter);
  }

  void ascend(){
    y--;
    x += (int)(Math.random() * 4 - 2);
  }

  void top(){
    if( y + diameter <= 0 ){
      y = height + diameter/2;
    }
  }
}