Nullpointer exception in LinkedList while using for-each loop

Question

I came across very odd Java behaviour, and I don\'t know if it is a bug, or am I missing something.

The code simply goes through the stateStack (LinkedList) list and

Answer 1

This is the internal implementation of LinkedList.ListItr.next():

public E next() {
    checkForComodification();
    if (!hasNext())
        throw new NoSuchElementException();

    lastReturned = next;
    next = next.next;   // your stacktrace says the NullPointerException happens here
    nextIndex++;
    return lastReturned.item;
}

The NullPointerException happens because the internal variable next is null; however, it seems that hasNext() is validating that there is a next element.

It seems to me that:

• you have more than one thread modifying your list, OR
• you are modifying your list in the implementation of destroy() while iterating over the list.

If you update your answer with your implementation of destroy() as sugested by @mthmulders, I either update, correct or delete my answer.