How to avoid "ConcurrentModificationException" while removing elements from `ArrayList` while iterating it?

Use an Iterator and call remove():

Iterator<String> iter = myArrayList.iterator();

while (iter.hasNext()) {
    String str = iter.next();

    if (someCondition)
        iter.remove();
}

As an alternative to everyone else's answers I've always done something like this:

List<String> toRemove = new ArrayList<String>();
for (String str : myArrayList) {
    if (someCondition) {
        toRemove.add(str);
    }
}
myArrayList.removeAll(toRemove);

This will avoid you having to deal with the iterator directly, but requires another list. I've always preferred this route for whatever reason.

Java 8 user can do that: list.removeIf(...)

    List<String> list = new ArrayList<>(Arrays.asList("a", "b", "c"));
    list.removeIf(e -> (someCondition));

It will remove elements in the list, for which someCondition is satisfied