We can use the same code and try to remove an element from the vector within the while-loop by invoking remove on the vector directly.
Output:
Exception in
thread "main" java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:444)
at java.util.AbstractList$Itr.next(AbstractList.java:417)
at tr.main(tr.java:16)
This means that while you are iterating over a vector, there is no way that the vector may be structurally modified by any other thread having a reference to that vector.