- Super: Object
This is a class which provides a multiple {@link Deque} compatible interface where every element within the queue is unique as if it were a member of a {@link Set}. Note that the subdeques can be given elements that are shared in multiple deques. In the returned {@link Deque}, elements which are removed will be removed from the other {@link Deque}s. As such, clearing of one {@link Deque} may result in other ones getting smaller in size. {@code null} elements are not permitted. This class is not thread safe.