Boundary Collisions

float x;
float xSpeed;
float y;
float ySpeed;

void setup() {
  size(500, 500);
  x = width/2;
  xSpeed = random(20);
  y = height/2;
  ySpeed = random(10);
}

void draw() {
  background(0);
  ellipse(x, y, 30, 30);
  x = x + xSpeed;
  y = y + ySpeed;
  boundaryCollisions();
  println(xSpeed);
}

void boundaryCollisions() {
  if (x > width - 15) {
    xSpeed = xSpeed*-1;
  }
  if (x < 15) {
    xSpeed = xSpeed*-1;
  }
  if (y > height-15) {
    ySpeed = ySpeed*-1;
  }
  if (y < 15) {
    ySpeed = ySpeed*-1;
  }
}