The java.util.Deque interface is a subtype of thejava.util.Queue interface. The Deque is related to the double-ended queue that supports addition or removal of elements from either end of the data structure, it can be used as aqueue (first-in-first-out/FIFO)or as astack (last-in-first-out/LIFO).

Methodsof deque:

1. add(element): Adds an element to the tail.
2. addFirst(element): Adds an element to the head.
3. addLast(element): Adds an element to the tail.
4. offer(element): Adds an element to the tail and returns a boolean to explain if the insertion was successful.
5. offerFirst(element): Adds an element to the head and returns a boolean to explain if the insertion was successful.
6. offerLast(element): Adds an element to the tail and returns a boolean to explain if the insertion was successful.
7. iterator(): Returna an iterator for this deque.
8. descendingIterator(): Returns an iterator that has the reverse order for this deque.
9. push(element): Adds an element to the head.
10. pop(element): Removes an element from the head and returns it.
11. removeFirst(): Removes the element at the head.
12. removeLast(): Removes the element at the tail.

 Deque deque = new LinkedList<>();

        // We can add elements to the queue in various ways
        deque.add("Element 1 (Tail)"); // add to tail
        deque.addFirst("Element 2 (Head)");
        deque.addLast("Element 3 (Tail)");
        deque.push("Element 4 (Head)"); //add to head
        deque.offer("Element 5 (Tail)");
        deque.offerFirst("Element 6 (Head)");
        deque.offerLast("Element 7 (Tail)");
 System.out.println(deque + "\n");

        // Iterate through the queue elements.
        System.out.println("Standard Iterator");
        Iterator iterator = deque.iterator();
        while (iterator.hasNext())
            System.out.println("\t" + iterator.next());


        // Reverse order iterator
        Iterator reverse = deque.descendingIterator();
        System.out.println("Reverse Iterator");
        while (reverse.hasNext())
            System.out.println("\t" + reverse.next());

        // Peek returns the head, without deleting
        // it from the deque
        System.out.println("Peek " + deque.peek());
        System.out.println("After peek: " + deque);

        // Pop returns the head, and removes it from
        // the deque
        System.out.println("Pop " + deque.pop());
        System.out.println("After pop: " + deque);

        // We can check if a specific element exists
        // in the deque
        System.out.println("Contains element 3: " +
                        deque.contains("Element 3 (Tail)"));

        // We can remove the first / last element.
        deque.removeFirst();
        deque.removeLast();
        System.out.println("Deque after removing " +
                            "first and last: " + deque);