What is the best way to remove objects from a List

Question

I have the following logic to remove inactive users in the system, since we cannot remove a row while iterating on the list. Is there a better way to handle this?

List<User> users = new ArrayList<User>();
List<User> removeUsers = new ArrayList<User>();

for (User user : users) {
  if (!user.isActive()) {
      removeUsers.add(user);
  }
}

users.removeAll(removeUsers);

Answer 1

I realize this is an old question, but it came up in a search I was doing, so others might still be getting here. With Java 8, the easiest way is to use the new "removeIf" method on the Collection class like so:

users.removeIf(user -> !user.isActive());

Easy peasy! It should be noted that, under the covers, the Java code is using Iterator.remove().

Oracle documentation

Answer 2

You could do:

for (int i = users.size()-1; i >= 0; i--) {
  if (!users.get(i).isActive()) {
    users.remove(i);
  }
}

Answer 3

If you use ArrayList, best way is Jeff M's variant. You may also use your variant, but you should consider to use Set (HashSet or IdentityHashSet) intstead of ArrayList for removeUser. For large amount of data it will have better performance.

But for LinkedList best way will be to use Iterator.remove method:

for (Iterator<User> it = users.iterator(); it.hasNext();)
    if (it.next().isActive())
        it.remove();