processing4/java/examples/Books/Nature of Code/chp4_systems/ParticleSystemInheritance_pushpop/ParticleSystem.pde

// The Nature of Code
// Daniel Shiffman
// http://natureofcode.com

class ParticleSystem {
  ArrayList<Particle> particles;
  PVector origin;

  ParticleSystem(PVector location) {
    origin = location.get();
    particles = new ArrayList<Particle>();
  }

  void addParticle() {
    float r = random(1);
    if (r < 0.5) { 
      particles.add(new Particle(origin));
    } 
    else {
      particles.add(new ParticleChild(origin));
    }
  }

  void run() {
    for (int i = particles.size()-1; i >= 0; i--) {
      Particle p = particles.get(i);
      p.run();
      if (p.isDead()) {
        particles.remove(i);
      }
    }
  }
}