问试图产生不重叠的气泡。为什么这个不行？

EN

ArrayList<Bubble> bubbles = new ArrayList<Bubble>();

void setup() {
  size(500, 500);
  background(210);

  for (int i = 0; i < 100; i++) {

    Bubble bubble = new Bubble();

    for (Bubble b : bubbles) {

      float d = dist(b.pos.x, b.pos.y, bubble.pos.x, bubble.pos.y);

      while (d < 40) { // which means 2 * r (radius of bubble)
        bubble.ChangePos();
        d = dist(b.pos.x, b.pos.y, bubble.pos.x, bubble.pos.y);
      }
    }

    bubbles.add(bubble);
  }

  for (Bubble b : bubbles) {
    fill(255, 0, 90, 50);
    b.Display();
  }
}

class Bubble {

  PVector pos = new PVector(random(width), random(height));
  float r = 20;

  void Display() {
    ellipse(pos.x, pos.y, r * 2, r * 2);
  }

  void ChangePos() {
    pos.set(random(width), random(height));
  }
}