Pong - problems with boundary check

Processing Coding Questions
11

Thank you!

I am having a problem accessing paddle.x.

In my main program I create a paddle and then I create a ball, passing to it the paddle.

I can access paddle.x fine in the main program and in my Ball constructor. But when I try to access it elsewhere in my Ball class it throws null pointer exception.

Here is my current code:

Ball ball;
Paddle paddle;


void setup() {
  size(640, 480);
  paddle = new Paddle();
  ball = new Ball(paddle);
 // println(paddle.x); prints paddle.x
}

void draw() {
  background(0);
  paddle.draw();
  paddle.move();
  
  paddle.checkBoundaries();
  
  ball.draw();
  ball.move();
}


class Paddle {
  public float x;
  public final float y = 440;
  
  float speedX;
  
  public Paddle() {
    x = 0;
    
  }
  
  public void move() {
    x = mouseX;
  }
  
  public void draw() {
    fill(255);
    rect(x, y, 100, 20);
  }
  
  public void checkBoundaries(){
    if(x < 0){
      x = 0;
    }
    
    if(x > (width - 100)){
     x = width - 100; 
    }
  }
}

class Ball {
  float xPos =0;
  float yPos = 0;
  
  float xSpeed = 2.8;
  float ySpeed = 2.2;
  
  int xDirection = 1;
  int yDirection = 1;
  
  int rad = 16;
  
  final float speed = 5;
  
  Paddle paddle;
  
  public Ball(Paddle paddle){
    paddle = paddle;
    
    // set starting position of the ball, start in center of screen
    xPos = width / 2;
    yPos = height / 2;
   // println(paddle.x); prints paddle.x
    
  }
  
  
  public void move() {
    // update the ball's position
    xPos +=  (xSpeed * xDirection);
    yPos +=  (ySpeed * yDirection);
    // println(paddle.x); throws null pointer exception
 
  }
  
  public void draw() {
    ellipse(xPos, yPos, rad, rad);
    checkBoundaries();
  }
  
  public void checkBoundaries() {
    //// check collision between ball and paddle, 100 = paddle length
    //if(xPos > paddle.x){
    ////if(xPos > paddle.x && xPos < (paddle.x + 100) && (yPos + 20) >= paddle.y) {
    //  xSpeed = abs(xSpeed) * -1; 
    //  ySpeed = abs(ySpeed) * -1; 
    //}
    println(paddle.x);
    
     
    
    if(xPos > width - rad) {
     xSpeed = abs(xSpeed) * -1; 
    }
    
    if(xPos < rad) {
     xSpeed = abs(xSpeed); 
    }
    
    if(yPos > height - rad) {
     ySpeed = abs(ySpeed) * -1; 
    }
    
    // check lower screen boundary
    //if(yPos < rad) {
    // ySpeed = abs(ySpeed); 
    //}
  }
  
  public void checkCollision() {
    
  }
}

Paddle and Ball are included together above.

So I am confused about passing objects in processing. I had to use globals to make this work. Instead - as above - what I really want to do is have the ball know about the paddle. But after passing to the constructor when I try to access paddle.x I get null pointer.

Note: I am using all public and no getter/setters for simplicities sake.