Using remove on a list inside a for each loop inside a while loop

Question

I have an assignment where I'm to create a race simulator. I have 8 objects stored in a list. I need to see when one of the objects crosses the finish line and remove them from the list and put them in another list. For this, I'm using a for each loop. I need to perform this check each time one takes a step so, therefore, the foreachloop is inside a while loop. When everyone has crossed the finish line the while loop shall stop and end the race.

while (lista.size()>0) {
        for (RaceTurtle raceTurtle : lista) {
            raceTurtle.raceStep();
            if(raceTurtle.getX() > RaceWindow.X_END_POS) {
                lista.remove(raceTurtle);
                winners.add(raceTurtle);
            }
            w.delay(10);
        }
    }

I have tried to use an iterator but it only throws me the same error. I have also tried to use a copy of the original list but that don't seem to work since it's inside a while loop.

Would apreciate if someone could give me an example of how this is to be done.

Tried again with iterator and this time it worked.

while (lista.size()>0) {
        for (Iterator<RaceTurtle> iterator = lista.iterator(); iterator.hasNext();) {
            RaceTurtle temp = iterator.next();
            temp.raceStep();
            if (temp.getX()> RaceWindow.X_END_POS) {
                winners.add(temp);
                iterator.remove();
            }
        }
        w.delay(50);
    }

Possible duplicate of [Iterating through a Collection, avoiding ConcurrentModificationException when removing objects in a loop](https://stackoverflow.com/questions/223918/iterating-through-a-collection-avoiding-concurrentmodificationexception-when-re) — Logan, May 19 '19 at 22:35
Tried with the example there and it worked, weird because I tried with an iterator before and it did not work. — w474490, May 19 '19 at 22:45

score 0 · Answer 1 · answered May 19 '19 at 22:42

0

If you are getting an ArrayIndexOutOfBoundsException or something similar to that, consider breaking the while loop inside the for loop if the list is empty. For example:

outer: // label the loop
while (lista.size()>0) {
    for (RaceTurtle raceTurtle : lista) {
        raceTurtle.raceStep();
        if(raceTurtle.getX() > RaceWindow.X_END_POS) {
            lista.remove(raceTurtle);
            winners.add(raceTurtle);
        }
        if (lista.size()>0) {
            break outer; // end the outer loop, preventing
                         // the possible iteration of nothing
        }
        w.delay(10);
    }
}

answered May 19 '19 at 22:42

Vincent Harris

70
10

Thx for the quick answer but this solved it for me: – w474490 May 19 '19 at 22:46
while (lista.size()>0) { for (Iterator iterator = lista.iterator(); iterator.hasNext();) { RaceTurtle temp = iterator.next(); temp.raceStep(); if (temp.getX()> RaceWindow.X_END_POS) { winners.add(temp); iterator.remove(); } } w.delay(50); } – w474490 May 19 '19 at 22:47
Is it not possible to format code in comments? Adding solution in original post. – w474490 May 19 '19 at 22:48

Using remove on a list inside a for each loop inside a while loop

1 Answers1