Actually, here a better quote:

"The iterators returned by this class's (ArrayList) iterator  and listIterator
methods are fail-fast: if list  is structurally modified at any time after the
iterator is created, in any way except through the iterator's own remove or
add methods, the iterator will throw a ConcurrentModificationException. Thus,
in the face of concurrent modification, the iterator fails quickly and
cleanly, rather than risking arbitrary, non-deterministic behavior at an
undetermined time in the future. "