Table of Contents

1. Queue Interface

The Queue interface is part of the Java Collections Framework and is used to hold multiple elements prior to processing. Queues typically, but not necessarily, order elements in a FIFO (First-In-First-Out) manner.

Common Implementations:

• LinkedList: Implements the Queue interface and provides methods for queue operations.
• PriorityQueue: An unbounded priority queue based on a priority heap.

Key Methods:

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

Example Using Queue Interface:

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

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

        // Add elements to the queue
        queue.add(1);
        queue.add(2);
        queue.add(3);

        // Display elements
        System.out.println("Queue: " + queue);

        // Remove an element
        int removed = queue.remove();
        System.out.println("Removed element: " + removed);

        // Display the head element
        int head = queue.peek();
        System.out.println("Head of the queue: " + head);

        // Display elements after removal
        System.out.println("Queue after removal: " + queue);
    }
}

2. Set Interface