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If that line gives you a NullPointer, then that means that getWorld() returns null. getWorld() returns null if the actor is not in the world. (getWorld()essentially says "Give me my world" and in that case the actor does not have a world.) So either your actor has not been inserted into the world, or it has been removed from it. So make sure that printNumberOfOrganisms() does not get called while the actor is not in the world.

aww =(

Sounds like two items of state: 1. An index into the array 2. A counter to measure how much time (how many act() cycles) have elapsed So, you declared these as fields. Then in your act() method you check the counter, and see whether the required time has elapsed: if (counter == 0) { .... If the time has elapsed then you do whatever you want with the appropriate item in the array. If that doesn't help, I guess you need to make your question more specific :)

@JL235 *facepalm* thank you =) @delmar thank you, its always good to see a shorter way of writing the code

That's exactly what I needed, thanks! I'm working on multiple scenarios right now, and I really appreciate all the help!