Retrieves, but does not remove, the head of the queue represented by
this deque (in other words, the first element of this deque).
This method differs from {@link #peek peek} only in that it throws an
exception if this deque is empty.
<p>This method is equivalent to {@link #getFirst()}.
@return the head of the queue represented by this deque
@throws NoSuchElementException if this deque is empty
Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from {@link #peek peek} only in that it throws an exception if this deque is empty.
<p>This method is equivalent to {@link #getFirst()}.
@return the head of the queue represented by this deque @throws NoSuchElementException if this deque is empty