As a Computer Science Student, you may have learned about many different Data Structure concepts, like Linked Lists, Stacks, Trees, etc., and you might even know about the Queue Concept. But, are you familiar with the “Priority Queue Concept in Java”?
As you know, the Data Structure Concept can be implemented using any programming language. The Priority Queues are not different from those that are a sub-category of the simple Queue Structure, where the Priority of elements plays a key role.
The same thing happens to the Priority Queue in Java. Several elements will make a queue along with a special value. Among them, whoever has the highest special value will first come out of the queue. Still have doubts? Hire a Java assignment helper to clear your doubts.
In this article, we will discuss Priority Queues along with the simple implementation process in the Java Programming Language. So, let us start the discussion.
TL;DR: Priority Queue In Java
Aspect | Summary |
Definition | A Priority Queue is a special queue where elements are processed based on priority, not just insertion order. |
Core Principle | The Higher-priority elements are removed first. If there are elements with the same priority, then they will follow the FIFO order. |
Pre-requisites | Understanding of Linked Lists, functions, and recursion basics. |
Types | Min Priority Queue (ascending order) and Max Priority Queue (descending order). |
Operations | En-Queue (Insertion) and De-Queue (Deletion) based on priority. |
What Is A Priority Queue In Java? Read More
The Priority Queue is a concept in Data Structures. You might have heard about the Queue Data Structure Concept, where a structural similarity is present with the Stack Concept. Just the Queue Data Structure concept follows the First In, First Out Principle.
The Priority Queue doesn’t follow the FIFO Principle. The Insertion & deletion of the elements depend upon another parameter that is known as the Priority. Based on the Priority, the elements get inserted or deleted.
If any element that has the highest priority is inserted at the end of the queue, it will be first removed from the system. In this way, the complete process goes on.
It has some properties. Depending upon the properties, the operations are performed. They are:
- Each element is associated with a priority value. And, elements are inserted based on their priority. That is, higher-priority elements are served first.
- An element with high priority is dequeued before an element with low priority.
- However, if elements with the same priority occur, they are served according to their order in the queue.
How Priority Queue Works With Java?
Internally, the Priority Queue is implemented with the Binary Heap in Java. Java, by default, follows the Min Heap process. The smallest element is placed at the root, and it has the highest priority.
As the priority queue follows the Heap Structure, it is best suited for insertion and removal. The Priority Queue belongs to the Queue interface, which can be extended to Collection and Iterable interfaces.
The Priority Queue with the heap structure can perform the following basic operations:
- Insertion: The element will be placed at the end. The time complexity will be O(log n).
- Deletion: The root will be removed, and the heap will be rebalanced. Time complexity is O(log n).
- Access: The top element will be returned without removal, and the time complexity is O(1).
What Are Different Types Of Priority Queues?
Priority Queue Java can mainly be differentiated into two types. According to the Priority with the number, the divisions are following two types:
1. Minimum Priority Queue Or Ascending Order Priority Queue:
In this type, the minimum number gets the highest priority. On the other hand, the maximum number in the queue gets the minimum priority. That is why this type of Priority Queue appears in the Ascending Order. That is why sometimes it is called an Ascending Order Priority Queue.
Suppose, in a queue, the number 1 gets the priority 10 & number 10 gets the priority 1. Same number 2 gets priority 9 & number 9 gets priority 2. So, what will be the structure of the queue? It will be in ascending order like 1,2,3,4….,10. The number with the highest priority appears at the beginning.
2. Maximum Priority Queue Or Descending Order Priority Queue:
It is just the opposite of the Minimum Priority Queue. In this type of Priority Queue, the minimum number gets the lowest priority. On the other hand, the maximum number in the queue gets the highest priority. That is why this type of Priority Queue appears in the Descending Order. This is the reason it is called a Descending Order Priority Queue.
Suppose, in a queue, the number 10 gets the priority 10 & number 1 gets the priority 1. The same number 9 gets priority 9 & number 2 gets priority 2. So, what will be the structure of the queue? It will be in descending order like 10,9,8,7….,1. The number with the highest priority appears at the beginning.
How To Initialize a Priority Queue In Java?
Before we go into any further discussion, we have to understand the simple process to initialize the Priority Queue in Java. If you are thinking of implementing a Priority Queue using a Linked List in Java, that will be discussed later. Here, we are going to discuss a surprise for you.
Have you ever thought that the Priority Queue can be implemented within Two Statements in the Main Function of Java? If you have not yet thought, it is time to look at the process. There is a special package present in Java for the same.
General Syntax: PriorityQueue<Integer> Name = new PriorityQueue<>();
import java.util.PriorityQueue; // Importing Queue Package
public class Main {
public static void main(String[] args) {
PriorityQueue<Integer> PQ = new PriorityQueue<>(); // Creating Priority Queue
}}
In the above example, the PriorityQueue Package in Java is used. It is a built-in package that comes with different built-in functions. Let us check the following functions that can be used with the help of the PriorityQueue Package.
- Add(Element): This is the Function used for the Insertion Operation in the Priority Queue Concept. Here, within the braces, the element’s name should be provided to add the value.
- Poll(): The Poll() Function is used to Remove Elements from the Priority Queue. Here, we don’t need to provide the element number. The top-most element will automatically be deleted.
- Peek(): The Peek() is the function that is used for accessing the elements from the Priority Queue. The Peek() Function will access the topmost element by default.
- Offer(): This also inserts elements into the priority queue. If the insertion fails, then it will return False, which is something different from Add().
- Remove(): This will remove the element and return the head value. If the queue is empty, it will throw the exception.
- Element(): This returns the head of the priority queue. It doesn’t remove or change the structure of the queue.
