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Homework 4 (due Sunday, September 27, 2015)

This homework is just two programming practice sections, both due Sunday.

Assignment 1: Take the following code we worked on in class, that produces a grid of randomly-colored Balls. Modify it so that the colors in the grid are a rainbow, like in the in-class assignment. One possible set of modifications:

  • Add a parameter color c to the Ball constructor function, and set this.c equal to that parameter.
  • Modify setup to add a hue variable that increases with every ball created.
class Ball {
  float x, y;
  float vx, vy;
  float size = 10;
  color c;
  Ball(float x, float y) {
    this.x = x;
    this.y = y;
    c = color(random(255), 255, 255);
    vx = random(1);
    vy = random(1);
  void draw() {
    ellipse(x, y, size*2, size*2);
  void move() {
    x += vx;
    y += vy;
    if (x < size || x > width-size) {
      vx = -vx;
    if (y < size || y > height-size) {
      vy = -vy;

ArrayList<Ball> list;

void setup() {
  size(500, 500);

  list = new ArrayList<Ball>();

  for (int x = 20; x < width-20; x += 20) {      
    for (int y = 20; y < height-20; y += 20) {
      list.add(new Ball(x, y));

void draw() {
  for (int i = 0; i < list.size(); i += 1) {

Assignment 2: Multipong! In this assignment, you'll start writing the code for the classic arcade game Pong. If you're not familiar with Pong, you can play it online at!

We've already got a Ball class, but we also need "paddles" for the players to control that the balls will bounce from. Write a Paddle class that’s a template for a paddle, just like the Ball class is a template for a ball.

The class will be very similar to Ball, but there are a few key differences:

  1. Paddles are shaped as a rectangle instead of a circle
  2. Paddles only move up and down, that is, veritcally -- there's no horizontal motion

Create two paddle instances, one at each side of the canvas, a paddle's width away from the edge; they should bounce up and down.

Submit a single processing file with a Ball and Paddle class in it, that has one or more bouncing balls and two bouncing paddles.

Here’s one way your sketch might look when run.

You can’t perform that action at this time.