🎓 Top 15 Udemy Courses (80-90% Discount): My Udemy Courses - Ramesh Fadatare — All my Udemy courses are real-time and project oriented courses.

▶️ Subscribe to My YouTube Channel (178K+ subscribers): Java Guides on YouTube

▶️ For AI, ChatGPT, Web, Tech, and Generative AI, subscribe to another channel: Ramesh Fadatare on YouTube

The Java Deque interface, short for "Double Ended Queue," is part of the Java Collections Framework, and it resides in java.util package.

Important Key Points About Deque Interface

Double Ended:

As the name suggests, Deque is a queue in which we can insert and remove elements from both ends. It means you can perform operations at the front as well as at the rear.

Insertion and Removal Operations:

Deque supports the insertion of elements at both ends. The methods addFirst(E e), addLast(E e), offerFirst(E e), and offerLast(E e) are used for this purpose. Similarly, to remove elements, we use removeFirst(), removeLast(), pollFirst(), and pollLast().

Exception throwing and Non-Exception throwing methods:

Similar to the Queue, each operation in Deque has two methods: one throws an exception when the operation fails (addFirst, removeLast etc.), and the other returns a special value (null or false, depending on the operation) without throwing an exception (offerFirst, pollLast etc.).

Stack LIFO operations:

The Deque interface can also function as a stack (LIFO). The Deque implementations have methods for push, pop, and peek operations when used as a stack.

No Capacity Restrictions:

Deques generally do not have any capacity constraints and they can grow as needed based on the usage, but ArrayDeque has an exception, as it is array-based.

Null Elements:

Depending on the implementation, null elements may or may not be allowed. For example, LinkedList allows nulls, but ArrayDeque does not.

Iteration:

Deque interface provides an iterator that can iterate in both directions - regular order via iterator() and reverse order via descendingIterator().

Usage in real-world applications:

Deque is often used in algorithm design and data structure implementation where you need more flexibility than a traditional queue or stack.

Thread Safety:

Similar to Queue, Deque implementations (ArrayDeque, LinkedList) are not thread-safe. The ConcurrentLinkedDeque is a thread-safe Deque implementation provided by Java.

Deque interface Methods

Deque Interface Hierarchy Diagram

ArrayDeque implementation of Deque Interface Examples

Java ArrayDeque Example

import java.util.ArrayDeque;
import java.util.Deque;

public class ArrayDequeExample {
    public static void main(String[] args) {
     // Creating Deque and adding elements
     Deque<String> deque = new ArrayDeque<String>();
     deque.add("element1");
     deque.add("element2");
     deque.add("element3");
     // Traversing elements
     for (String str : deque) {
        System.out.println(str);
     }
   }
}

Output:

element1
element2
element3

Java ArrayDeque Example: offerFirst() and pollLast()

package com.javaguides.collections.queueexamples;

import java.util.ArrayDeque;
import java.util.Deque;

public class DequeExample {
    public static void main(String[] args) {
        Deque <String> deque = new ArrayDeque < String > ();
        deque.offer("element1");
        deque.offer("element2");
        deque.add("element3");
        deque.offerFirst("element4");
        System.out.println("After offerFirst Traversal...");
        for (String s: deque) {
            System.out.println(s);
        }
        // deque.poll();
        // deque.pollFirst();//it is same as poll()
        deque.pollLast();
        System.out.println("After pollLast() Traversal...");
        for (String s: deque) {
            System.out.println(s);
        }
    }
}

Output:

After offerFirst Traversal...
element4
element1
element2
element3
After pollLast() Traversal...
element4
element1
element2

Reference

https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/util/Deque.html

https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/util/ArrayDeque.html

My Top and Bestseller Udemy Courses. The sale is going on with a 70 - 80% discount. The discount coupon has been added to each course below:

Spring Boot + RabbitMQ Course - The Practical Guide

Java Collections Framework – The Deque Interface

Important Key Points About Deque Interface

Double Ended:

Insertion and Removal Operations:

Exception throwing and Non-Exception throwing methods:

Stack LIFO operations:

No Capacity Restrictions:

Null Elements:

Iteration:

Usage in real-world applications:

Thread Safety:

Deque interface Methods

Deque Interface Hierarchy Diagram

ArrayDeque implementation of Deque Interface Examples

Java ArrayDeque Example

Java ArrayDeque Example: offerFirst() and pollLast()

Output: After offerFirst Traversal... element4 element1 element2 element3 After pollLast() Traversal... element4 element1 element2

Reference

My Top and Bestseller Udemy Courses. The sale is going on with a 70 - 80% discount. The discount coupon has been added to each course below:

Build REST APIs with Spring Boot 4, Spring Security 7, and JWT

[NEW] Learn Apache Maven with IntelliJ IDEA and Java 25

ChatGPT + Generative AI + Prompt Engineering for Beginners

Spring 7 and Spring Boot 4 for Beginners (Includes 8 Projects)

Building Real-Time REST APIs with Spring Boot - Blog App

Building Microservices with Spring Boot and Spring Cloud

Java Full-Stack Developer Course with Spring Boot and React JS

Build 5 Spring Boot Projects with Java: Line-by-Line Coding

Testing Spring Boot Application with JUnit and Mockito

Spring Boot Thymeleaf Real-Time Web Application - Blog App

Master Spring Data JPA with Hibernate

Spring Boot + Apache Kafka Course - The Practical Guide

Java Testing: Mastering JUnit 5 Framework

Reactive Programming in Java: Spring WebFlux and Testing

Spring Boot + RabbitMQ Course - The Practical Guide

Functional Programming in Java (Includes Java Collections)

ChatGPT for Java Developers: Boost Your Productivity with AI

Comments

Post a Comment

Spring Boot 3 Paid Course Published for Free on my Java Guides YouTube Channel

Output:

`After offerFirst Traversal... element4 element1 element2 element3 After pollLast() Traversal... element4 element1 element2`

Spring Boot 3 Paid Course Published for Free
on my Java Guides YouTube Channel