Why am I not getting a java.util.ConcurrentModificationException in this example?

Question

Note: I am aware of the Iterator#remove() method.

In the following code sample, I don\'t understand why the List.remove in main

Answer 1

The forward/iterator method does not work when removing items. You can remove the element without error, but you will get a runtime error when you try to access removed items. You can't use the iterator because as pushy shows it will cause a ConcurrentModificationException, so use a regular for loop instead, but step backwards through it.

List integerList;
integerList = new ArrayList();
integerList.add(1);
integerList.add(2);
integerList.add(3);

int size= integerList.size();

//Item to remove
Integer remove = Integer.valueOf(3);

A solution:

Traverse the array in reverse order if you are going to remove a list element. Simply by going backwards through the list you avoid visiting an item that has been removed, which removes the exception.

//To remove items from the list, start from the end and go backwards through the arrayList
//This way if we remove one from the beginning as we go through, then we will avoid getting a runtime error
//for java.lang.IndexOutOfBoundsException or java.util.ConcurrentModificationException as when we used the iterator
for (int i=size-1; i> -1; i--) {
    if (integerList.get(i).equals(remove) ) {
        integerList.remove(i);
    }
}