class CircleDraw {
  float x, y, r, a;

  void drawSelf() {
     fill(255);
     noStroke();
     ellipse(x + r * cos(a), y - r * sin (a), 5, 5);
     a += 0.1;

     if (a >= 2 * PI) {
       background(100);
       a = 0;
     }
  }
}

CircleDraw c;

void setup() {
  size (400, 400);

  c = new CircleDraw();
  c.x = width / 2;
  c.y = height / 2;
  c.r = 100;
  c.a = 0;
}

void draw() {
  c.drawSelf();
}