Learning Processing: A Beginner's Guide to Programming Images ...

430 Learning Processing
void draw() {
particles.add(new Particle());
background(255);
// Iterate through our ArrayList and get each Particle
for (int i = 0; i < particles.size(); i + + ) {
Particle p = (Particle) particles.get(i);
p.run();
p.gravity();
p.display();
}
// Remove the first particle when the list gets over 100.
if (particles.size() > 100) {
particles.remove(0);
If the ArrayList has more than 100 elements
}
in it, we delete the fi rst element, using
}
remove().
// A simple Particle class
class Particle {
float x;
float y;
float xspeed;
float yspeed;
Particle() {
x = mouseX;
y = mouseY;
xspeed = random(–1,1);
yspeed = random(–2,0); }
void run() {
x = x + xspeed;
y = y + yspeed;
}
void gravity() {
yspeed + = 0.1;
}
void display() {
stroke(0);
fill(0,75);
ellipse(x,y,10,10);
}
}
A new Particle object is added to the
ArrayList every cycle through draw().
The ArrayList keeps track of how many
elements it is storing and we iterate
through them all.