A basic processing sketch for nick

ball.pde

int x,y, xVelocity; // our three variables that we need to keep track of
void setup(){
  size(320,240); //size of the app
  smooth(); // makes circles anti aliased
  noStroke(); // means there is no outer line on our circle
  fill(100,100,150); // the colour of the ball
  background(240); // the background
  xVelocity = 1;
  x = width/2; // width is the width of the sketch its always available
  y = height/2; // same with height
}
void draw(){
  background(240);
  if(x > width || x < 0){// if the x is greater than the width of the sketch (x > width) or (||) if the x is less than zero (x < 0)
    xVelocity *= -1;// change the xvelocity to its inverse, so for this case it will be 1 or -1
  }
  x += xVelocity; // increase the x by the xVelocity
  ellipse(x,y,20,20); // draw an ellipse 20px wide and high at x and y
}