Hey fairly new at this and im trying to find out why my code would be giving be a null pointer exception, im not really sure what this error code means so i'm having alot of trouble solving it heres my code;

Roomba player;
void setup() {
 size(600,600);
}

void draw() {
 // blank the background
 background(0);
 player.drawRoomba(); -This is where i get the error

}
class Roomba {
 int roombaX;
 int roombaY;
 int dX;
 int dY;

 Roomba () {
   roombaX = 300;
   roombaY = 300;
   dX = 0;
   dY = 0;
 }

 void drawRoomba() {
   fill(50,125,10,150);
   ellipse(roombaX,roombaY,50,50);

   // move the player
   roombaX += dX;
   roombaY += dY;
 }  

 void keyPressed() {
   // up
   if (key == 'i') {
     dY--;
   }
   // down
   if (key == 'k') {
     dY++;
   }
   // left
   if (key == 'j') {
     dX--;
   }
   // right
   if (key == 'l') {
     dX++;
   }
   // press space for brakes!
   if (key == ' ') {
     dX = (int)(dX * 0.9);
     dY = (int)(dY * 0.9);
   }
   if (roombaX < 0 || roombaX > 600) {
     dX *= -1;
   }
   if (roombaY < 0 || roombaY > 600) {
     dY *= -1;
   }
 }

}

Any help would be greatly appreciated im having alot of trouble here.

when you do new Roomba(); in your setup, it means that you allocate memory to that object, so it will remember whats in it.
thats a reason why we use objects, we need to keep specific informations in memory for each objects.