Collections: Iterator.remove is the only safe removal during a loop

Iterator.remove keeps the iterator's internal state consistent while removing, but calling the list's own remove during a for-each still trips the fail-fast check on the next step and throws ConcurrentModificationException.

Code

List<Integer> nums = new ArrayList<>(List.of(1, 2, 3, 4, 5, 6));
Iterator<Integer> it = nums.iterator();
while (it.hasNext()) {
    if (it.next() % 2 == 0) {
        it.remove();
    }
}
System.out.println("Evens removed safely: " + nums);
try {
    for (Integer n : nums) {
        if (n == 1) {
            nums.remove(n);
        }
    }
} catch (ConcurrentModificationException e) {
    System.out.println("Removing via the list during for-each throws: " + e.getClass().getSimpleName());
}

Output

Evens removed safely: [1, 3, 5]
Removing via the list during for-each throws: ConcurrentModificationException