Summary of Java Queue

Introduction to Java Queue

A Queue is a collection designed for holding elements prior to processing. It follows the FIFO (First In First Out) principle, meaning the first element added is the first one to be removed.

Key Concepts

• Interface: java.util.Queue is an interface in Java that defines the operations of a queue.
• Implementations: Common implementations of the Queue interface include:
  • LinkedList: A doubly-linked list that can be used as a queue.
  • PriorityQueue: An implementation that orders elements based on their natural ordering or a comparator.

Key Methods

• add(E e): Inserts the specified element into the queue. Throws an exception if the queue is full.
• offer(E e): Inserts the specified element into the queue. Returns false if the queue is full.
• remove(): Retrieves and removes the head of the queue. Throws an exception if the queue is empty.
• poll(): Retrieves and removes the head of the queue, returning null if the queue is empty.
• peek(): Retrieves, but does not remove, the head of the queue. Returns null if the queue is empty.

Example Usage

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

public class QueueExample {
    public static void main(String[] args) {
        Queue<String> queue = new LinkedList<>();
        
        // Adding elements to the queue
        queue.add("Element 1");
        queue.add("Element 2");
        queue.offer("Element 3");
        
        // Accessing and removing elements
        System.out.println("Head of queue: " + queue.peek()); // Output: Head of queue: Element 1
        System.out.println("Removed from queue: " + queue.remove()); // Output: Removed from queue: Element 1
        System.out.println("Next head of queue: " + queue.poll()); // Output: Next head of queue: Element 2
    }
}

Conclusion

The Queue interface is essential for scenarios where order of processing matters. Understanding how to use the Queue and its methods is crucial for effective data manipulation in Java applications.