addFirst
void addFirst(E e)
Inserts the specified element at the front of this deque if it is possible to do so immediately without
violating
capacity restrictions. When using a capacity-restricted deque, it is generally preferable to use
method offerFirst
(E).
pollLast
E pollLast()
Retrieves and removes the last element of this deque, or returns null if this deque is empty.
Returns:
the tail of this deque, or null if this deque is empty