Class Balloon

//balloon
Balloon b;
Balloon [] a = new Balloon [3];

void setup () {
  size (500, 500);
  b = new Balloon (250, 250, 100);
  a [0] = new Balloon (100, 300, 50);
  a [1] = new Balloon (400, 300, 50);
  a [2] = new Balloon (250, 400, 20);
}

void draw () {
  background (255);
  b.display();
  a[0].display();
  a[1].display();
  a[2].display();
  b.move_up();
  a[0].move_up();
  a[1].move_up();
  a[2].move_up();
}

class Balloon {
  int x;
  int y;
  int r;

  Balloon (int x, int y, int r) {
    this.x = x;
    this.y = y;
    this.r = r;
  }

  void display () {
    fill (255, 255, 0);
    line (x, y, x, y+r);
    ellipse (x, y, r, r);
  }

  void move_up () {
    this.y = this.y -1;
    if (this.y <= 10) {
      this.y = height;
    }
  }
}