Bouncing Ball

int numBalls = 3;
Ball b[] = new Ball [numBalls];

void setup() {
  size(600, 400);
  for (int i = 0; i < 3; i++) {
    b[i] = new Ball(random(600), random(300, 400), 20);
  }
}

void draw() {
  background(0);

  for (int i = 0; i < 3; i++) {
    b[i].generate();
    b[i].moveBall();
  }
}

class Ball {
  float ballR, ballX, ballY;
  float speedY = 2;
  float speedX = 2;
  float colour = 100;
  float colour2 = 100;
  float colour3 = 100;

  Ball(float x, float y, float r) {
    this.ballX = x;
    this.ballY = y;
    this.ballR = r;
  }

  float getX() {
    return ballX;
  }

  float getY() {
    return ballY;
  }
  float getR() {
    return ballR;
  }
  void flipSpeedX() {
    speedX = -speedX;
  }

  void flipSpeedY() {
    speedY = -speedY;
  }

  void generate() {
    fill(colour, colour2, colour3);
    ellipse(ballX, ballY, ballR, ballR);
  }

  void changeColour() {
    colour = random(255);
    colour2 = random(255);
    colour3 = random(255);
    generate();
  }

  void moveBall() {
    ballX += speedX;
    ballY+= speedY;

    if (ballY > height ) {
      speedY = -speedY;
      changeColour();
    } else if (ballY <= 0) {
      speedY = -speedY;
      changeColour();
    }
    if (ballX > width ) {
      speedX = -speedX;
      changeColour();
    } else if (ballX <= 0) {
      speedX = -speedX;
      changeColour();
    }
  }
}