Returns a
Set view of the mappings contained in this map. The
set is backed by the map, so changes to the map are reflected in the
set, and vice-versa. The set supports element removal, which removes
the corresponding mapping from the map, via the
Iterator.remove, Set.remove, removeAll,
retainAll, and clear operations. It does not support
the add or addAll operations.
The view's iterator is a "weakly consistent" iterator
that will never throw
ConcurrentModificationException,
and guarantees to traverse elements as they existed upon
construction of the iterator, and may (but is not guaranteed to)
reflect any modifications subsequent to construction.
Warning: the iterator associated with this Set
requires the creation of
java.util.Map.Entry objects with each
iteration. The
NonBlockingHashtable does not normally create or
using
java.util.Map.Entry objects so they will be created soley
to support this iteration. Iterating using
#keySet or
#values will be more efficient.