RainStormSystem Processing Program

RainDrop.java

// A simple Particle class

class RainDrop {
  int x;
  int y;

  RainDrop(int startX, int startY) {
    this.x = startX;
    this.y = startY;
  }

  void run() {
    update();
    display();
  }

  // Method to update position
  void update() {
    y += 3;
  }

  // Method to display
  void display() {
    noStroke();
    fill(240, 240, 255, 100);
    ellipse(this.x, this.y, 2, 8);
  }

  // Is the drop still around?
  boolean isDone() {
    if (this.y > height) {
      return true;
    } else {
      return false;
    }
  }
}

RainStorm.java

// A class to describe a group of Particles
// An ArrayList is used to manage the list of Particles 

class RainStorm {
  ArrayList<RainDrop> drops;
  int startY = 0;
  int endY = height;

  RainStorm() {
    this.drops = new ArrayList<RainDrop>();
  }

  void addDrop() {
    int startX = (int) random(0, width);
    drops.add(new RainDrop(startX, startY));
  }

  void run() {
    for (int i = drops.size()-1; i >= 0; i--) {
      RainDrop drop = drops.get(i);
      drop.run();
      if (drop.isDone()) {
        drops.remove(i);
      }
    }
  }
}

RainStormSystem.java

/**
 * Raindrops are generated each cycle through draw()
 * and fade over time.
 * A RainStorm object manages a variable size (ArrayList) 
 * list of raindrop. 
 */

RainStorm rainStorm;

void setup() {
  size(640, 360);
  rainStorm = new RainStorm();
}

void draw() {
  background(72, 102, 112);
  rainStorm.addDrop();
  rainStorm.run();
}