how to remove object from stream in foreach method?

Streams are designed to be used in a more functional way, preferably treating your collections as immutable.

The non-streams way would be:

arrB.addAll(arrA);arrA.clear();

However you might be using Streams so you can filter the input so it's more like:

arrB.addAll(arrA.stream().filter(x -> whatever).toList())

then remove from arrA (thanks to @Holgar for the comment).

arrA.removeIf(x -> whatever)

If your predicate is expensive, then you could partition:

Map<Boolean, XXX> lists = arrA.stream()  .collect(Collectors.partitioningBy(x -> whatever));arrA = lists.get(false);arrB = lists.get(true);

or make a list of the changes:

List<XXX> toMove = arrA.stream().filter(x->whatever).toList();arrA.removeAll(toMove);arrB.addAll(toMove);

As the others have mentioned, this is not possible with foreach - as it is impossible with the for (A a: arrA) loop to remove elements.

In my opinion, the cleanest solution is to use a plain for while with iterators - iterators allow you to remove elements while iterating (as long as the collection supports that).

Iterator<A> it = arrA.iterator()while (it.hasNext()) {    A a = it.next();    if (!check(a))        continue;    arrB.add(a);    it.remove();}

This also saves you from copying/cloning arrA.

I don't think you can remove from arrA while you iterate over it.

You can get around this by wrapping it in a new ArrayList<>();

new ArrayList<>(arrA).stream().foreach(c -> {arrB.add(c); arrA.remove(c);});