Returns a {@link 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. If the map is modified
while an iteration over the set is in progress (except through
the iterator's own <tt>remove</tt> operation, or through the
<tt>setValue</tt> operation on a map entry returned by the
iterator) the results of the iteration are undefined. The set
supports element removal, which removes the corresponding
mapping from the map, via the <tt>Iterator.remove</tt>,
<tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
<tt>clear</tt> operations. It does not support the
<tt>add</tt> or <tt>addAll</tt> operations.
Its {@link Spliterator} typically provides faster sequential
performance but much poorer parallel performance than that of
{@code HashMap}.
@return a set view of the mappings contained in this map
Returns a {@link 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. If the map is modified while an iteration over the set is in progress (except through the iterator's own <tt>remove</tt> operation, or through the <tt>setValue</tt> operation on a map entry returned by the iterator) the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt> operations. It does not support the <tt>add</tt> or <tt>addAll</tt> operations. Its {@link Spliterator} typically provides faster sequential performance but much poorer parallel performance than that of {@code HashMap}.
@return a set view of the mappings contained in this map