Java Deque Interface

The Deque interface of the Java collections framework provides the functionality of a double-ended queue. It extends the Queue interface.

There are 2 different classes in Deque interface.

  1. ▪ ArrayDeque
  2. ▪ LinkedList

Working of Deque

In a regular queue, elements are added from the rear and removed from the front. However, in a deque, we can insert and remove elements from both front and rear.


How to use Deque

we must import the java.util.Deque package to use Deque.


                    // Array implementation of Deque
                    Deque<String> animal1 = new ArrayDeque<>();

                    // LinkedList implementation of Deque
                    Deque<String> animal2 = new LinkedList<>();

Some of the commonly used methods of the Deque interface are:

  1. ◈ addFirst() - Adds the specified element at the beginning of the deque. Throws an exception if the deque is full.
  2. ◈ addLast() - Adds the specified element at the end of the deque. Throws an exception if the deque is full.
  3. ◈ offerFirst() - Adds the specified element at the beginning of the deque. Returns false if the deque is full.
  4. ◈ offerLast() - Adds the specified element at the end of the deque. Returns false if the deque is full.
  5. ◈ getFirst() - Returns the first element of the deque. Throws an exception if the deque is empty.
  6. ◈ getLast() - Returns the last element of the deque. Throws an exception if the deque is empty.
  7. ◈ peekFirst() - Returns the first element of the deque. Returns null if the deque is empty.
  8. ◈ peekLast() - Returns the last element of the deque. Returns null if the deque is empty.
  9. ◈ removeFirst() - Returns and removes the first element of the deque. Throws an exception if the deque is empty.
  10. ◈ removeLast() - Returns and removes the last element of the deque. Throws an exception if the deque is empty.
  11. ◈ pollFirst() - Returns and removes the first element of the deque. Returns null if the deque is empty.
  12. ◈ pollLast() - Returns and removes the last element of the deque. Returns null if the deque is empty.