What Is Queue Data Structure in Java?

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Scott Campbell

What Is Queue Data Structure in Java?

A queue is a fundamental data structure in computer science that follows the First-In-First-Out (FIFO) principle. It is similar to a real-life queue where the first person who joins the line is the first one to be served. In Java, the Queue interface provides methods for adding elements to the end of the queue and removing elements from the beginning.

The Queue Interface

The Queue interface in Java is part of the java.util package and extends the Collection interface. It defines several methods, including:

  • add(element): Adds an element to the end of the queue.
  • remove(): Removes and returns the element at the front of the queue.
  • element(): Retrieves, but does not remove, the element at the front of the queue.
  • peek(): Retrieves, but does not remove, the element at the front of the queue (returns null if empty).
  • isEmpty(): Checks if the queue is empty.
  • size(): Returns the number of elements in the queue.

The LinkedList Class Implementation

In Java, one common implementation of a queue is using a linked list. The LinkedList class provides a convenient way to implement a queue by utilizing its methods:

  • offer(element): Adds an element to the end of the queue.
  • poll(): Removes and returns the element at the front of the queue.

Here’s an example of how to create and use a queue using LinkedList:


import java.util.LinkedList;
import java.Queue;

public class QueueExample {
    public static void main(String[] args) {
        Queue queue = new LinkedList<>();

        // Adding elements to the queue
        queue.offer("Apple");
        queue.offer("Banana");
        queue.offer("Cherry");

        // Removing elements from the queue
        String firstElement = queue.poll();
        System.out.println("Removed: " + firstElement);

        // Peeking at the first element in the queue
        String peekedElement = queue.peek();
        System.println("Peeked: " + peekedElement);
    }
}

The output of this code snippet will be:


Removed: Apple
Peeked: Banana

Conclusion

The Queue data structure in Java provides an efficient way to manage elements based on their arrival order. By utilizing methods like add, remove, and peek, you can easily implement a FIFO behavior in your programs. Remember to choose an appropriate implementation, like using a linked list with the LinkedList class, based on your specific requirements.

Now that you have a better understanding of the queue data structure in Java, you can efficiently handle scenarios where processing elements in a specific order is crucial.

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