What basic operations on a Map are permitted while iterating over it?

Question

Say I am iterating over a Map in Java... I am unclear about what I can to that Map while in the process of iterating over it. I guess I am mostly confused by this warning in

Answer 1

There is no global answer. The map interface let the choice to the users. Unfortunately, I think that all the implementations in the jdk use the fail-fast implementation (here is the definition of fail-fast, as it stated in the HashMap Javadoc):

The iterators returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove method, 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.