Trying to learn coding for fun, I get nullpointerexception when I try to compile the code.  First time using Processing also, sorry if my coding is lacking :(  My goal is to be able to create an ellipse with physics and collision on a mouse release.  Thank you in advance :)

int defBalls = 0;
int numBalls = 10;
float spring = 0.05;
float gravity = 0.03;
Ball[] balls = new Ball[numBalls];
int[] y = new int[numBalls];
int[] x = new int[numBalls];
float ranBall = random(10, 40);

void setup()
{
 size(200, 800);
 noStroke();
 smooth();
}

void draw() {
 background(0);
 for (int i = 0; i < numBalls; i++) {
   balls[i].collide();
   balls[i].move();
   balls[i].display();  
 }
}

class Ball {
 float x, y;
 float diameter;
 float vx = 0;
 float vy = 0;
 int id;
 Ball[] others;

 Ball(float xin, float yin, float din, int idin, Ball[] oin) {
   x = xin;
   y = yin;
   diameter = din;
   id = idin;
   others = oin;
 }
 
 void collide() {
   for (int i = id + 1; i < numBalls; i++) {
     float dx = others[i].x - x;
     float dy = others[i].y - y;
     float distance = sqrt(dx*dx + dy*dy);
     float minDist = others[i].diameter/2 + diameter/2;
     if (distance < minDist) {
       float angle = atan2(dy, dx);
       float targetX = x + cos(angle) * minDist;
       float targetY = y + sin(angle) * minDist;
       float ax = (targetX - others[i].x) * spring;
       float ay = (targetY - others[i].y) * spring;
       vx -= ax;
       vy -= ay;
       others[i].vx += ax;
       others[i].vy += ay;
     }
   }  
 }
 
 void move() {
   vy += gravity;
   x += vx;
   y += vy;
   if (x + diameter/2 > width) {
     x = width - diameter/2;
     vx += -0.9;
   }
   else if (x - diameter/2 < 0) {
     x = diameter/2;
     vx *= -0.9;
   }
   if (y + diameter/2 > height) {
     y = height - diameter/2;
     vy *= -0.9;
   }
   else if (y - diameter/2 < 0) {
     y = diameter/2;
     vy *= -0.9;
   }
 }
 
 void display() {
   fill(255);
   ellipse(x, y, diameter, diameter);
 }
}

void mouseReleased() {
   addBall(mouseX, mouseY);
 }

void drawBall(int index) {
 fill(255);
 ellipse(x[index], y[index], ranBall, ranBall);
}

void addBall(int newX, int newY) {
 if (defBalls < numBalls) {
   x[defBalls] = newX;
   y[defBalls] = newY;
   defBalls++;
 }
}

Thank you kind sir, you rock and thank you for being a moderator on the forum.