// An ArrayList is used to manage the list of Particles 
  
  class ParticleSystem {
  
    ArrayList particles;    // An arraylist for all the particles
    PVector origin;        // An origin point for where particles are birthed
  
    ParticleSystem(int num, PVector v) {
      particles = new ArrayList();              // Initialize the arraylist
      origin = v.get();                        // Store the origin point
      for (int i = 0; i < num; i++) {
        // We have a 50% chance of adding each kind of particle
        if (random(1) < 0.5) {
          particles.add(new CrazyParticle(origin)); 
        } else {
          particles.add(new Particle(origin)); 
        }
      }
    }
  
    void run() {
      // Cycle through the ArrayList backwards b/c we are deleting
      for (int i = particles.size()-1; i >= 0; i--) {
        Particle p = (Particle) particles.get(i);
        p.run();
        if (p.dead()) {
          particles.remove(i);
        }
      }
    }
  
    void addParticle() {
      particles.add(new Particle(origin));
    }
  
    void addParticle(Particle p) {
      particles.add(p);
    }
  
    // A method to test if the particle system still has particles
    boolean dead() {
      if (particles.isEmpty()) {
        return true;
      } 
      else {
        return false;
      }
    }
  
  }