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A Priority Queue In Java is used when the objects are supposed to be processed based on the priority. This article will help you explore this concept in detail. Following pointers will be covered in this article,
So let us get started then,
As mentioned already, a PriorityQueue is used when the objects are supposed to be processed based on the priority. It is known that a queue follows First-In-First-Out algorithm, but sometimes the elements of the queue are needed to be processed according to the priority, that’s when the PriorityQueue comes into play. The PriorityQueue is based on the priority heap. The elements of the priority queue are ordered according to the natural ordering, or by a Comparator provided at queue construction time, depending on which constructor is used.Few important points on Priority Queue are as follows:
Moving on with this article on Priority Queue in Java
public interface Queue<E> extends Collection<E>
Moving on with this article on Priority Queue in Java
Method | Description |
boolean add(object) | It is used to insert the specified element into this queue and return true upon success. |
boolean offer(object) | It is used to insert the specified element into this queue. |
Object remove() | It is used to retrieves and removes the head of this queue. |
Object poll() | It is used to retrieves and removes the head of this queue, or returns null if this queue is empty. |
Object element() | It is used to retrieves, but does not remove, the head of this queue. |
Object peek() | It is used to retrieves, but does not remove, the head of this queue, or returns null if this queue is empty. |
Moving on with this article on Priority Queue in Java
package com.journaldev.collections;
import java.util.Comparator; import java.util.PriorityQueue; import java.util.Queue; import java.util.Random; public class PriorityQueueExample { public static void main(String[] args) { //natural ordering example of priority queue Queue<Integer> integerPriorityQueue = new PriorityQueue<>(7); Random rand = new Random(); for(int i=0;i<7;i++){ integerPriorityQueue.add(new Integer(rand.nextInt(100))); } for(int i=0;i<7;i++){ Integer in = integerPriorityQueue.poll(); System.out.println("Processing Integer:"+in); } //PriorityQueue example with Comparator Queue<Customer> customerPriorityQueue = new PriorityQueue<>(7, idComparator); addDataToQueue(customerPriorityQueue); pollDataFromQueue(customerPriorityQueue); } //Comparator anonymous class implementation public static Comparator<Customer> idComparator = new Comparator<Customer>(){ @Override public int compare(Customer c1, Customer c2) { return (int) (c1.getId() - c2.getId()); } }; //utility method to add random data to Queue private static void addDataToQueue(Queue<Customer> customerPriorityQueue) { Random rand = new Random(); for(int i=0; i<7; i++){ int id = rand.nextInt(100); customerPriorityQueue.add(new Customer(id, "Pankaj "+id)); } } //utility method to poll data from queue private static void pollDataFromQueue(Queue<Customer> customerPriorityQueue) { while(true){ Customer cust = customerPriorityQueue.poll(); if(cust == null) break; System.out.println("Processing Customer with ID="+cust.getId()); } } }
Output:
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