Priority Queue vs Normal Queue

In this post, we will learn the difference between Priority Queue and Normal Queue in Java. This is a frequently asked question in Java interviews for beginners. Let's dive into it.

Difference between Priority Queue and Normal Queue in Java

Feature	Priority Queue	Normal Queue
Ordering	A Priority Queue orders elements based on their priority, where elements with higher priority are dequeued first.	A normal Queue follows the First-In-First-Out (FIFO) order, where elements are dequeued in the order they were enqueued.
Element Comparison	Elements in a Priority Queue must be comparable or use a custom Comparator to determine their priority.	Element comparison is not required for a normal Queue, as elements are dequeued in the order they were added.
Internal Data Structure	Priority Queue is often implemented using a binary heap or a priority heap to efficiently maintain the order of elements based on their priority.	Normal Queue is typically implemented using a dynamic array or a linked list.
Methods	Priority Queue may offer additional methods for managing priority, such as offer(), poll(), and peek().	Normal Queue typically provides basic methods like offer(), poll(), peek(), and size().
Use Cases	Priority Queue is suitable when elements have varying levels of importance or urgency, and they need to be processed based on their priority.	Normal Queue is commonly used for implementing tasks like breadth-first search, task scheduling, or holding elements for processing in the order they were received.
Performance	Priority Queue operations like insertion and removal have O(log n) complexity due to the heap-based implementation.	Normal Queue operations have O(1) complexity for insertion and removal, making them more efficient.
Example	Priority Queue Example: Processing tasks based on their priority level.	Normal Queue Example: Processing messages in the order they arrived.

In summary, a Priority Queue is designed to manage elements based on their priority, making it useful for scenarios where the order of processing is determined by priority levels. On the other hand, a normal Queue follows the First-In-First-Out (FIFO) order, making it suitable for situations where elements are processed in the order they were added. The choice between a Priority Queue and a normal Queue depends on the specific requirements and characteristics of the data being processed.