Deque

    /**
     * Retrieves and removes the head of the queue represented by this deque
     * (in other words, the first element of this deque), or returns
     * <tt>null</tt> if this deque is empty.
     *
     * <p>This method is equivalent to {@link #pollFirst()}.
     *
     * @return the first element of this deque, or <tt>null</tt> if
     *         this deque is empty
     */
    E poll();

    /**
     * Pops an element from the stack represented by this deque.  In other
     * words, removes and returns the first element of this deque.
     *
     * <p>This method is equivalent to {@link #removeFirst()}.
     *
     * @return the element at the front of this deque (which is the top
     *         of the stack represented by this deque)
     * @throws NoSuchElementException if this deque is empty
     */
    E pop();

两者的区别不大，仅仅是pop()比poll()多了一个判断：元素为null，抛出异常，源码如下

if (x == null) throw new NoSuchElementException();
        return x;