Game loop logic?

Question

Hey all,
I'm looking for some help in the logic department instead of specific code help;
I'm currently working (or trying, anyway) to make a Java ME game for my mobile. Essentially, it's a little arcade shooter: ship shoots asteroid, you get the idea. The setup is pretty simple;
There's the game loop that takes care of all the usual things: input, collision detection, etc. There's my little ship that can fire bullets. Firing the bullets is easily done but it gets a bit odd with the shooting of the bullets. Right now, I simply have an array of 10 bullets. When the player presses fire, the first bullet not on the screen is selected and fired, by placing it at the top of the ship and then moving it forward. The forward movement is done by a method in the game loop called moveBullet(). With each game loop iteration, regardless of where the 10 bullets are, they simply get 5 pixels added to their Y location and the new position is set for the sprite. This all works like a charm, so there's no question there.
It gets tricky, however, when I would like to introduce an enemy ship. Again, placing the enemy ship isn't the problem. In fact, if I want it to fire whenever the player fires, this too works just fine. I have simply copied the above setup from the player and applied it to the enemy. The thing is, however, that if I want to create a game with different missions (and thus: different amount of enemies per mission), I do not want to run about 10 or 20 moveEnemyBullet() methods in my main game loop. (Especially not when they're not all being used!) I would want something more CPU efficient.
So, my question is: how can I create a way of letting the enemies fire their bullets whenever they feel like it (I'll write AI for that) but let the movement only activate for that enemy iteration when it's needed, instead of running all the time, eating up CPU cycles?

Answer 1

Thanks, doubld!
Funnily enough, I talked this problem over with a friend last night and he suggested nearly the very same thing! Only difference was to place all created bullets in a vector, and then loop through the vector to fire off all the bullets their respective moveBullets method. The reason for that suggestion was because I indicated I wanted to have multiple weapon types but still would like to fire them all through one loop, perhaps each weapon with its own behaviour. (Say: have custom bullets, but also have heatseeking missiles.) He suggested creating an interface called Weapon and have all weapon classes implement this, like so:
public interface Weapon {
     void createWeapon() throws IOException;
     void fireWeapon();
     void moveWeapon();
     void destroyWeapon();
     Sprite getWeaponSprite();
}And then call all the movement methods (or other shared methods) and have different types of weapons all in the same vector, firing off in one game loop, like so:
for(int i=0; i < weaponVector.size(); i++)
     ((Weapon) weaponVector.elementAt(i)).moveWeapon();
}This way, each weapon that's created is in the vector and can be removed once used (as you said: either by hitting the player / enemy or by moving off the screen).
All in all, I think, because or the different behaviours I want per weapon, I'm going with the variant suggested by my friend. However, it's very good to hear two very different people with a technical background give roughly the same advice. That gives me a good idea that I'm on the right way. :)