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Mastering Queue Data Structure in Java: A Comprehensive Guide

Introduction to Queue Data Structure

Do you ever find yourself standing in a long line waiting for your turn to be served? The people in front of you get their turn first, and you have to wait your turn patiently.

The Queue data structure functions just like that. A Queue is a linear data structure that follows the first-in-first-out (FIFO) principle.

In other words, the person that enters the queue first is the one that gets served first.

Implementing a Queue in Java can be effortless as it comes with the built-in Queue interface in the java.util package. In this article, we will discuss how to implement a Queue in Java using a LinkedList.

Real-world example of Queue

Imagine you are in a long line at the movie ticket counter. The first person in the line will get their tickets first, and then the second person, and so on.

This is a real-life example of a Queue. Every time a new person gets in line, they are added to the end, and when a person gets their tickets, they are removed from the front.

Implementing a Queue in Java

To implement a Queue in Java, we use the Queue interface in the java.util package. In this tutorial, we will use a LinkedList implementation to create a Queue.

Code Block for Queue implementation using LinkedList

Step 1: Instantiating Queue reference using LinkedList

To create a new Queue in Java using a LinkedList, you need to declare a new Queue reference and instantiate using the new keyword and the LinkedList class. Here is the code snippet:

Queue queue = new LinkedList<>();

After this line of code, we have an empty Queue of type String.

Step 2: Using add method to append elements to the Queue

To add elements to the Queue, we use the add method. The add method adds the specified element to the Queue.

Here is the code snippet:


If the Queue has space, this method returns true. If the Queue is full, it can throw an IllegalStateException or NullPointerException.

Step 3: Displaying the Queue using System.out.println statement

To display the current status of the Queue, we use the System.out.println statement, as shown below:


This statement prints out the elements in the Queue, in a readable format. Step 4: Removing elements from the Queue using remove and poll methods

To remove elements from the Queue, we use either the remove method or the poll method.

The remove method deletes the head element from the Queue, while the poll function returns the head element from the Queue and removes it if found. Here is the code snippet:

queue.remove(); //removes the head element

queue.poll(); //deletes the head element and returns it

If the Queue is empty, the remove method throws a NoSuchElementException, while the poll method simply returns null.

Step 5: Checking the topmost element using peek function

To check the head element of the Queue without deleting it, we use the peek function. Here is the code snippet:


If the Queue is empty, the peek function throws the NoSuchElementException.

Step 6: Using size function to obtain the size of leftover elements

To know the size of the leftover elements in the Queue, we use the size function. Here is the code snippet:


The Collection interface contains this function, which returns the size of the Queue as the number of elements it contains.


In this tutorial, we have discussed what Queue data structure is, a real-life example of Queue and how to implement Queue using LinkedList in Java. We have also covered the key methods and functions used in the implementation of a Queue.

We hope you now have a better understanding of Queues and their uses. In this article, we have covered the concept of Queue data structure, including its real-world application as seen in a ticket line.

We have also reviewed how to implement a Queue in Java using the built-in Queue interface found in the java.util package, and specifically using LinkedList. The article highlighted key methods and functions used in Queue implementation such as add, remove, poll, peek, and size.

Understanding Queue data structure is crucial for programming applications that require data to enter or exit in a specific order. The takeaway from this article is that Queues are important data structures to handle ordered data processing.

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