int nb=10;

Balle[]balle=new Balle[nb];
void setup() {
  size(800, 700, P3D);
  for (int i=0;i<nb;i++) {
    balle[i]=new Balle(random(50, 500), random(50, 500));
  }
}

void draw() {
  background(255);
  for (int i=0;i<nb;i++) {
    balle[i].rebondir();
    balle[i].bouger();
  }
  for (int i=0;i<nb;i++) {
    for (int j = i + 1 ; j < nb; j++) {
      balle[i].collision(balle[j]);
    }
  }
  for (int i=0;i<nb;i++) {
    balle[i].dessiner();
  }
}

class Balle {
  PVector position;
  float deplacementX;
  float deplacementY;
  int rayon;
  boolean bing;

  Balle(float dx, float dy) {
    position = new PVector(dx, dy);
    deplacementX= random(-1, 1);
    deplacementY= random(-1, 1);
    rayon = 20;
    bing = false;
  }

  void rebondir() {
    if (position.x > width) {
      deplacementX = -1;
    }
    if (position.x < 0) {
      deplacementX = 1;
    }
    if (position.y >height) { 
      deplacementY = -1;
    }
    if (position.y < 0) {
      deplacementY =1;
    }
  }
  void bouger() {
    position.x += deplacementX;
    position.y += deplacementY;
    bing = false;
  }

  void dessiner() {
    if (bing) {
      fill(255, 0, 0);
    } 
    else {
      fill(255, 0, 255);
    }
    ellipse(position.x, position.y, 2 * rayon, 2 * rayon);
  }

  void collision(Balle balleExt) {
    float distance = position.dist(balleExt.position);
    if (distance < 2 * rayon) {
      bing = true;
      balleExt.bing = true;
    }
  }
}