Java IndexOutOfBoundsException

Question

I made an little shoot em up game..It works normal but I want also implement if fires intersects they will disappear. I have two list for Player bullets and for computer bullets ...But if I have more bullets from computer or reverse .Here my loop

     for (int i = 0; i < cb.size(); i++) {
        for (int j = 0; j < b.size(); j++) {
            if (b.get(j).rect.intersects(cb.get(i).rect)) {

                cb.remove(i);
                b.remove(j);


                continue;

            }
            if (cb.get(i).rect.intersects(b.get(j).rect)) {


                b.remove(j);
                cb.remove(i);

                continue;

            }

        }

    }

This is my game which woking algoritms... http://rapidshare.com/files/364597095/ShooterGame.2.6.0.jar

Answer 1

I highly recommend against playing with the for loop counters from within the loop itself. You are careful now, you won't be careful later ("let's try a hack here to debug") and end up with bugs.

One solution could be:

• check whether two objects intersect
• if they do, save a reference into a separate list of thingsToRemove
• finally, go through the thingsToRemove and remove (or set to 'null', or -1 or whatever) the corresponding elements in the cb and b lists

Answer 2

As stated in Carl's comment the second if should be redundant.

As for your IndexOutOfBounds exception, this is caused by the following: When a computer bullet hits a player bullet, you remove both from the lists. Using continue you then continue comparing the same computer bullet to the remaining player bullets. However, that computer bullet was already removed before! Hence, I suggest you break instead of continue, then the next computer bullet is checked for intersection with player bullets.

As Roman hints at with his code you should further decrease the outer loop's counter, as you reduced the list size by removing one of the bullets. Hence, what used to be bullet #3 is in the next iteration what previously was bullet #4. So after the break you don't want the increment of the outer loop's counter.