Vector empty item?

[libia]

Hi all,

I'm new here and I'm new to Java.
I'm working on a Java project for school. I want to use a Vector to store the positions of the cars, this works very good, until I need to remove a car..
To save memory en keep it running smooth, I want to remove a car when it rides offscreen, so I build a check like this:

if(p.x > 200) {
	cars.removeElementAt(0);
}

p is the Point I got from the vector (using a for-loop starting at int i = 0)
But once the first car is removed, the applet stops working, no crash or something, the screen just isn't refreshed or something..
to draw I use this:

int size = cars.size();
for(int i = 0; i < size; i++) {
	if(cars.get(i) != null) {
		Point p = (Point)cars.get(i);
		g.drawRect(p.x, p.y, 4, 2);
	}
}

I searched on google, and they say everywhere, that all items get shifted back when you remove an item from a Vector, so I guess it should work, also the != null check doesn't seem to work...

I hope you understand my story and that someone can tell me where it goes wrong, if you need more information, just ask please :)

Sorry for my English btw...

[libia]

oke, a quick response from me :P

I seem to have solved it already, but I don't think it's efficient the way I do it...
instead of removing an item, I do this:

cars.set(i, null);

can anyone tell me how efficient this is?