// Learning Processing
  // Daniel Shiffman
  // http://www.learningprocessing.com
  
  // Example 23-4: Super fancy ArrayList and rectangle particle system
  
  // A simple Particle Class
  class Particle {
    
    float x;
    float y;
    float xspeed;
    float yspeed;
    float life;
    
    // Make the Particle
    Particle(float tempX, float tempY) {
      x = tempX;
      y = tempY;
      xspeed = random(-1,1);
      yspeed = random(-2,0);
      life = 255;
    }
    
    // Move
    void run() {
      x = x + xspeed;
      y = y + yspeed;
    }
    
    // Fall down
    void gravity() {
      yspeed += 0.1;
    }
    
    // Stop moving
    void stop() {
      xspeed = 0;
      yspeed = 0;
    }
    
    // Ready for deletion
    boolean finished() {
      // The Particle has a "life" variable which decreases.
      // When it reaches 0 the Particle can be removed from the ArrayList.
      life -= 2.0; 
      if (life < 0) return true;
      else return false;
    }
    
    // Show
    void display() {
      // Life is used to fade out the particle as well
      stroke(0, life);
      fill(175,life);
      ellipse(x,y,10,10);
    }
  }