Queue is a fundamental data structure in Java that represents a collection of elements following the First-In, First-Out principle. Think of it like a line of people waiting - the first person to join the line is the first person to be served. In Java, Queue is an interface that extends the Collection interface.
The Queue interface defines several core methods for manipulating queue elements. For adding elements, we have add and offer methods - add throws an exception if the queue is full, while offer returns false. For removing elements, remove throws an exception if empty, while poll returns null. For examining the head element without removing it, element throws an exception if empty, while peek returns null. The offer, poll, and peek methods are generally preferred as they handle edge cases more gracefully.
Java provides several implementations of the Queue interface. LinkedList is a general-purpose implementation that also implements the Deque interface, allowing operations at both ends. ArrayDeque is a high-performance implementation using a resizable array, making it faster than LinkedList for most operations. PriorityQueue is special - it orders elements by their natural ordering or a provided comparator, so it doesn't strictly follow FIFO but rather serves the highest priority element first.
Here's a practical example of using Queue in Java. We start by importing java dot util package and creating a Queue instance using LinkedList implementation. We add elements using the offer method - First, Second, and Third. The peek method shows us the head element without removing it, which returns First. The poll method removes and returns the head element. Finally, we can check the remaining size of the queue. This demonstrates the FIFO behavior where elements are processed in the order they were added.
To summarize what we have learned about Queue in Java: Queue is a fundamental interface that follows the First-In-First-Out principle, making it perfect for ordered processing. The core methods offer, poll, and peek provide safe ways to add, remove, and examine elements. Common implementations like LinkedList and ArrayDeque give us flexibility in choosing the right performance characteristics. Queues are essential for many applications including task scheduling, breadth-first search algorithms, and any scenario requiring ordered element processing.