HansFrank HansFrank - 1 year ago 55
Java Question

Error on ArrayList

for IndexOutOfBoundsException:

Hi i'm making a space invader like game and i have a problem when a bullet
collides with the enemy.
Here is the code:

for (int i = 0; i < enemies.size(); i++) {
for (int j = 0; j < bullets.size(); j++) {
if (collidesWith(bullets.get(j), enemies.get(i))) { //Line 81 The Error Occurred here

Code for the Colliding:

public static boolean collidesWith(Entity collider, Entity collided) {
Rectangle hitBox1 = collider.getHitbox();
Rectangle hitBox2 = collided.getHitbox();

return hitBox1.intersects(hitBox2);

Code for the Hitbox:

public Rectangle getHitbox() {
return new Rectangle(getX(), getY(), getWidth(), getHeight());

The Error Messages:

Exception in thread "Thread-4" java.lang.IndexOutOfBoundsException: Index: 3, Size: 3
at java.util.ArrayList.rangeCheck(ArrayList.java:635)
at java.util.ArrayList.get(ArrayList.java:411)
at io.github.kjordo711.game.Main.run(Main.java:81)
at java.lang.Thread.run(Thread.java:724)

I think the error cause by 2 or more bullets hits the enemy

for OutOfMemoryError:

The Player can shoot too many bullets at once
if they hold Space the bullet will keep shooting without delaying
i could limit the bullet spawning but the problem is even with 10 bullets max on screen
the error still occur, i tried to delay it with


but it just sleep all the game thread

Answer Source

It's because you're removing object within the loops, which is not correct and besides ArrayIndexOutOfBoundsException this can cause a ConcurrentModificationExcetion, also.

When you're supposed to remove an object from a collection, consider using the java.util.Iterator interface.

Iterator<Enemy> enemiesIterator = enemies.iterator();
Iterator<Entity> bulletsIterator = bullets.iterator();
while (enemiesIterator.hasNext()) {
    Enemy nextEnemy = enemiesIterator.next();
    while(bulletsIterator.hasNext()) {
        Entity nextBullet = bulletsIterator.next();
        if (colliesWith(nextBullet, nextEnemy) {
Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download