Java Deque Interface

The Java Deque interface, short for “double-ended queue,” is a part of the Java Collections Framework. It extends the Queue interface and represents a linear collection that supports element insertion and removal at both ends. In other words, it provides a flexible way to work with a queue-like structure where elements can be added or removed from both the front and the back.

The Deque interface defines several methods for performing various operations on the double-ended queue, including:

1. Adding Elements:

• addFirst(E e) / offerFirst(E e): Inserts the specified element at the front of the deque.
• addLast(E e) / offerLast(E e): Inserts the specified element at the end of the deque.

1. Removing Elements:

• removeFirst() / pollFirst(): Removes and returns the first element from the deque.
• removeLast() / pollLast(): Removes and returns the last element from the deque.

1. Peeking Elements:

• getFirst() / peekFirst(): Retrieves the first element without removing it.
• getLast() / peekLast(): Retrieves the last element without removing it.

1. Stack-like Operations:

• push(E e): Adds an element to the front of the deque (similar to stack’s push operation).
• pop(): Removes and returns the first element from the front of the deque (similar to stack’s pop operation).

The Deque interface is implemented by several classes in Java, including:

• ArrayDeque: A resizable array-based implementation of a double-ended queue.
• LinkedList: A linked-list-based implementation of a double-ended queue.

Here’s an example of how you might use the Deque interface:

import java.util.*;

public class DequeExample {
    public static void main(String[] args) {
        Deque<String> deque = new LinkedList<>(); // You can also use ArrayDeque

        deque.addLast("Element 1");
        deque.addFirst("Element 2");
        deque.addLast("Element 3");

        System.out.println(deque); // Output: [Element 2, Element 1, Element 3]

        System.out.println(deque.pollFirst()); // Output: Element 2
        System.out.println(deque); // Output: [Element 1, Element 3]

        System.out.println(deque.peekLast()); // Output: Element 3
    }
}

Remember that the Deque interface provides both queue-like and stack-like operations, making it a versatile choice for scenarios where you need to manipulate elements from both ends of the collection.