ArrayList removeAll

Question

I have the following arraylists:

ArrayList<Obj o> list1 = new ArrayList<>();
ArrayList<String> list2 = new ArrayList<>();

I want to remove all of the elements from list1 that have (string)ID that equals the elements from list2.

if(o.getId().equals(one of the strings from list2)) -> remove.

How can I do that with removeAll or some other way without having to write an additional for. I'm searching for the most optimal way to do this.

Thank you in advance.

Answer 1

If you are using java 8, you could do:

ArrayList<YourClass> list1 = new ArrayList<>();
ArrayList<String> list2 = new ArrayList<>();

list1.removeIf(item -> list2.contains(item.getId()));
// now list1 contains objects whose id is not in list2

Assuming YourClass has a getId() method that returns a String.

---

For java 7, using iterator is the way to go:

Iterator<YourClass> iterator = list1.iterator();
while (iterator.hasNext()) {
    if (list2.contains(iterator.next().getId())) {
        iterator.remove();
    }
}