Queue

A Queue is a data structure that follows the First In, First Out (FIFO) principle. This means that the element that is inserted first will be the first to be removed, just like a queue in real life (e.g., standing in line at a ticket counter).

In Java, the Queue interface is a part of the java.util package and is used to represent a collection of elements that need to be processed in a specific order.

• Enqueue (add): Adds an element to the end of the queue.
• Dequeue (remove): Removes the element from the front of the queue.
• Peek: Retrieves, but does not remove, the element at the front of the queue.

Queue Operations

• offer(E e): Adds an element to the queue (returns true if the element is added successfully).
• poll(): Removes and returns the front element of the queue (returns null if the queue is empty).
• peek(): Retrieves the front element without removing it (returns null if the queue is empty).
• size(): Returns the number of elements in the queue.
• isEmpty(): Checks if the queue is empty.

Common Implementations of Queue

Java provides different ways to implement queues, and some of the most commonly used classes are:

• LinkedList: Implements both the List and Queue interfaces, making it suitable for a queue with dynamic size.
• PriorityQueue: A queue where elements are ordered according to their natural ordering or by a comparator provided at the time of construction.
• ArrayDeque: A resizable array implementation of the Deque interface, which allows elements to be added or removed from both ends of the queue.