Why does ArrayList not throw ConcurrentModificationException when modified from multiple threads?

Question

ConcurrentModificationException : This exception may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible.<

Answer 1

Because you are not using an iterator, there is no chance of a ConcurrentModificationException being thrown.

Calling remove(0) will simply remove the first element. It might not be the same element intended by the caller if another thread removes 0 before execution completes.