for (Ball j : balles) {
    for (Ball k : balles) {
      float distance = PVector.dist(j.getPos(), k.getPos());
      if (distance < 255) {
        stroke(distance);
        line(j.position.x, j.position.y, k.position.x, k.position.y );
      }
    }
  }

ArrayList<Ball> balles;

void setup() {
  size(800, 600, P3D);
  ellipseMode(CENTER);
  balles = new ArrayList<Ball>();
}

void draw() {
  background(255);
  for (Ball balle : balles) {
    balle.update();
  }

  for (Ball j : balles) {
    for (Ball k : balles) {
      float distance = PVector.dist(j.getPos(), k.getPos());
      if (distance < 255) {
        stroke(distance);
        line(j.position.x, j.position.y, k.position.x, k.position.y );
      }
      if (distance <= 40 && distance != 0){
        j.vitesse.x= -j.vitesse.x; 
        j.vitesse.y= -j.vitesse.y;
        //k.vitesse.x= -k.vitesse.x; 
        //k.vitesse.y= -k.vitesse.y;
      }
    }
  }
}

void mouseClicked() {
  PVector position, vitesse;
  position = new PVector( mouseX, mouseY );
  vitesse = new PVector( random(-5, 5), random(-5, 5) );
  balles.add( new Ball( position, vitesse ) );
}

class Ball {
  PVector position, vitesse;
  int rayon;
  
  Ball( PVector pos, PVector vit ) {
    position = pos.get();
    vitesse = vit.get();
    rayon = 40;
  }
  
  void update() {
    position.add(vitesse);
    if ( position.x > width-(rayon/2) || position.x < rayon/2 ) { 
      vitesse.x = -vitesse.x;
    }
    if ( position.y > height-(rayon/2) || position.y < rayon/2 ) { 
      vitesse.y = -vitesse.y;
    }
    fill(0);
    ellipse( position.x, position.y, rayon, rayon );
  }
  
  PVector getPos() {
    return position;
  }
}

 
class Object {
  Object() {}
}

PVector posb1 = new PVector( random(50,(width-50)), random(50,(height-50)) );    // position initiale balle b1
PVector velb1 = new PVector( random(-5, 5), random(-5, 5) );                     // velocite balle b1
float mb1 = 10;                                                                // masse balle b1
PVector posb2 = new PVector( (width-50), random(50,(height-50)) );    // position initiale balle b2
PVector velb2 = new PVector( random(-5, 5), random(-5, 5) );                     // velocite balle b2
float mb2 = 1; 
Ball b1 = new Ball( posb1, velb1, mb1 );
Ball b2 = new Ball( posb2, velb2, mb2 );  
Ball[] balles = { b1, b2 };

void setup()
{  
  ellipseMode(CENTER);
  size(200,200,P3D);
}

void draw()
{  
  background(255); 
  for( int i = 0; i < balles.length; i++)
  {
    balles[i].checkWall();
    if(i < balles.length-1){ balles[i].checkCollision(balles[i+1]); }
    balles[i].update();
    balles[i].display();
  }
}

class Ball
{  
  PVector position, velocite;
  float masse, diametre;
  Ball( PVector pos, PVector vel, float m )
  {
    position = pos.get();
    velocite = vel.get();
    masse = m/100.;
    diametre = sqrt(masse)*40;
  }

  void update()
  {
    position.add(velocite);  
  }
  
  void display()
  {
    fill(0);
    ellipse( position.x, position.y, diametre, diametre );
  }
  
  void checkWall()
  {  
    if( position.x >= width - (diametre/2) )
    {
      position.x -= ( position.x + (diametre/2) ) - width;
      velocite.x = - velocite.x;
    }

    if( position.x <= diametre/2 )
    {
      position.x = diametre/2 ;
      velocite.x = - velocite.x;
    }
    if( position.y >= height - (diametre/2) )
    {
      position.y -= (position.y + (diametre/2)) - height;
      velocite.y = - velocite.y;
    }
    if( position.y <= diametre/2 )
    {
      position.y = diametre/2 ;
      velocite.y = - velocite.y;
    }
  }
  
  void checkCollision(Ball other)
  {
    PVector bVect = PVector.sub(other.position, position);
    float bVectMag = bVect.mag();
    
    if ( bVectMag < (diametre/2) + (other.diametre/2) )
    {
      float theta  = bVect.heading();
      float sine = sin(theta);
      float cosine = cos(theta);

      PVector[] bTemp = { new PVector(), new PVector() };
      bTemp[1].x  = cosine * bVect.x + sine * bVect.y;
      bTemp[1].y  = cosine * bVect.y - sine * bVect.x;
      
      PVector[] vTemp = { new PVector(), new PVector() };
      vTemp[0].x  = cosine * velocite.x + sine * velocite.y;
      vTemp[0].y  = cosine * velocite.y - sine * velocite.x;
      vTemp[1].x  = cosine * other.velocite.x + sine * other.velocite.y;
      vTemp[1].y  = cosine * other.velocite.y - sine * other.velocite.x;
      
      PVector[] vFinal = { new PVector(), new PVector() };
      vFinal[0].x = ((masse - other.masse) * vTemp[0].x + 2 * other.masse * vTemp[1].x) / (masse + other.masse);
      vFinal[0].y = vTemp[0].y;
      vFinal[1].x = ((other.masse - masse) * vTemp[1].x + 2 * masse * vTemp[0].x) / (masse + other.masse);
      vFinal[1].y = vTemp[1].y;
      
      bTemp[0].x += vFinal[0].x;
      bTemp[1].x += vFinal[1].x;
      
      PVector[] bFinal = { new PVector(), new PVector() };
      bFinal[0].x = cosine * bTemp[0].x - sine * bTemp[0].y;
      bFinal[0].y = cosine * bTemp[0].y + sine * bTemp[0].x;
      bFinal[1].x = cosine * bTemp[1].x - sine * bTemp[1].y;
      bFinal[1].y = cosine * bTemp[1].y + sine * bTemp[1].x;
      
      other.position.x = position.x + bFinal[1].x;
      other.position.y = position.y + bFinal[1].y;
      position.add(bFinal[0]);
      
      velocite.x = cosine * vFinal[0].x - sine * vFinal[0].y;
      velocite.y = cosine * vFinal[0].y + sine * vFinal[0].x;
      other.velocite.x = cosine * vFinal[1].x - sine * vFinal[1].y;
      other.velocite.y = cosine * vFinal[1].y + sine * vFinal[1].x;
    }
  }
}