2) Create an array list of particles in your main program

• • • • Declare your ArrayList<Particle> as a global variable named particles.

      • In setup(), initialize particles.

      • In draw(), loop through particles.

        • Update each particle

      • In draw(), through particles a second time.

        • Render each particle

        • Explanation:  Why don't we just call update() and render() inside the same loop?  This is because (1) It's good style to separate our logic and display parts of our program and (2) Later on we'll remove particles using update(), and doing so will cause render() to crash the program when it tries to draw a particle that isn't there anymore.

      • Write the mousePressed() method.  Remember this is a special method in Processing which is called each time the user completes a full click.

        • Add one particle to the ArrayList

3) Improving Particles

• • • Movement

      • Add xSpeed and ySpeed variables to Particle 

      • In the constructor, assign them random starting values.

      • In the update() method, use them to change x and y position

    • Color

      • Add red, green, and blue variables to Particle

      • In the constructor, assign them random starting value

      •  In the update() method, use them to set the fill color

    • Gravity

      • Each frame, increase the particle's ySpeed by a set value to represent gravity

    • More Particles

      • In your mousePressed() method,  use a loop to add 30 particles instead of just one.
        
        

4) Counting Particles

• • • Add a text output to your program that displays the number of particles in your ArrayList

    • Notice that when you run the program, this number never goes down.  We'll need to add in code to remove extra particles from the list once they leave the screen!

5) Removing Particles

• • • In the particle's update method, it can remove itself from the ArrayList when it goes off the bottom of the screen.

    • To do so we'll use a special keyword:  this.  The keyword this simply means "me."  You an use the line of code below to say, "When I am below the screen, remove me from the list."
      
      

if(y > height)

{

particles.remove(this); 

}