remove elements from CopyOnWriteArrayList

Question

I am getting an exception when I try to remove elements from CopyOnWriteArrayList using an iterator. I have noticed that it is documented

Element-c

Answer 1

Iterate over the collection choosing all the elements you want to delete and putting those in a temporary collection. After you finish iteration remove all found elements from the original collection using method removeAll.

Would that work out for you? I mean, not sure if deletion logic is more complicated than that in your algorithm.

Answer 2

Ususlly you would iterate first gathering elemenet to be deleted in a separate list then delete them outside the for each loop (which is disguised iterator based loop anyway)

Answer 3

Below works fine with CopyOnWriteArrayList

for(String key : list) {
    if (<some condition>) {
        list.remove(key);
    }
}

Answer 4

Since this is a CopyOnWriteArrayList it is totally safe to remove elements while iterating with forEach. No need for fancy algorithms.

list.forEach(e -> {
    if (shouldRemove(e))
        list.remove(e);
});

EDIT: Well of course that works if you want to delete elements by reference, not by position.

Answer 5

You could use Queue instead of List.

private Queue<Something> queue = new ConcurrentLinkedQueue<Something>();

It's thread safe and supports iterator.remove(). Be aware of the thread-safe behavior of Queue iterators, though (check the javadoc).

Answer 6

If you want to delete all use just clear(). If you want to keep elements put them in a temporary ArrayList and get them back from there.

List<Object> tKeepThese= new ArrayList<>();
for(ListIterator<Object> tIter = theCopyOnWriteArrayList; tIter.hasNext();)
{
    tObject = tIter.next();
    if(condition to keep element)
        tKeepThese.add(tObject);
}
theCopyOnWriteArrayList.clear();
theCopyOnWriteArrayList.addAll(tKeepThese);