I actually just shared my own Asteroids clone (although it plays very different) on this forums https://forum.processing.org/topic/my-latest-creation

Anyways, what your looking to add is acceleration. When the player moves the acceleration is increased and when nothing is hit the player decelerates back to 0. You also want to have a limiter on have high the acceleration can go.

On second thought, I don't think the asteroids ship has a limit on acceleration...

The game's great, however that's not exactly what i'm looking for. I'm trying to make the ship rotate with keys, rather than the mouse. What I'm really looking for is something that will lock the ship's direction as long as the up key is held.

Nobody knows?

I see your player has a movang and a speed, and you update x and y according to these, so it should work as you intend, no? Speed decreases gradually, which is fine too. I am not sure where the problem is, and we cannot experiment to pinpoint the issue, since your code is incomplete.

The code works fine, the problem is that I would like the player to "drift" when the up key is released. What I mean by this is when you hold the up key, the player starts moving in the direction he is facing, however I don't want the player to turn when the left and right keys are pressed, just rotate. If the up key is then pressed again, the player will start accelerating in the new direction. If you need to run the code, I believe it should work by commenting out anything that has to do with enemies or bullets.

" I believe it should work by commenting out anything that has to do with enemies or bullets"
That's the kind of work you should have done yourself... But well, the code isn't so large, so I did it.
And when I run it, as I expected, I get the behavior you describe above, so I still don't understand where your problem is.

The problem is the behavior above is not what I want. I'm trying to mimic zero gravity, where when you accelerate forwards, simply turning doesn't change your direction. In order to travel in the direction you are facing, you need to apply thrust again. Here's an example:

I think the code that he/she has already does what he/she wants it just doesn't look like it's functioning correctly because the limit on max acceleration is to low, acceleration rate is too high, and player turn rate is too slow. At least that's what I got from running it.

What tfguy44 posted is exactly what I want, but I just need it to slow down when you're not holding a key. How would I go about doing this? I tried messing with it myself, but I can't get it.

You can dampen the ship's speed by a small amount each frame. This causes what feels like normal drag, and will eventually slow the ship to a stop.

Just throw these few line in:

Thanks!