Java Queue & Priority in Java

What is Queue in Java?

A Queue in Java is a data structure that follows the FIFO (First In First Out) principle. Elements are inserted at the rear (end) and removed from the front (beginning).

Objectives of Using Queue

Queue is used to manage tasks in order of arrival, implement scheduling algorithms, and store elements for sequential processing.

Advantages

Queues maintain the order of elements, are simple to implement with Java Collections, and are useful for buffering and task scheduling.

Limitations

Queues have limited access—only front and rear elements are accessible. They are not suitable for random access, and performance may vary with large datasets.

Queue in Java Process

To use Queue in Java, import java.util.Queue or java.util.LinkedList, create a Queue instance, use add()/offer() to insert elements, remove()/poll() to remove elements, and peek() to check the front element.

Example of Queue

Queue queue = new LinkedList<>();
queue.add("A");
queue.add("B");
queue.add("C");
System.out.println(queue.remove()); // Outputs: A
    

What is PriorityQueue in Java?

PriorityQueue is a special type of Queue where elements are ordered based on their priority rather than insertion order. By default, lower values have higher priority.

Objectives of PriorityQueue

PriorityQueue is used to manage tasks according to priority, handle urgent tasks first, and implement priority-based scheduling.

Advantages

PriorityQueue automatically orders elements by priority, is useful in simulations, scheduling, and task management, and allows efficient retrieval of the highest-priority element.

Limitations

PriorityQueue does not allow direct access to arbitrary elements, does not maintain insertion order for elements with the same priority, and performance may degrade with large data sets if comparator is complex.

Example of PriorityQueue

PriorityQueue pq = new PriorityQueue<>();
pq.add(30);
pq.add(10);
pq.add(20);
System.out.println(pq.poll()); // Outputs: 10 (highest priority)
    

Best Practices

Choose the Queue type depending on your requirements (FIFO vs Priority). Always handle empty queues to avoid exceptions, use appropriate collection classes for efficiency, and implement custom comparators if custom ordering is needed in PriorityQueue.