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Judul : What Is Priorityqueue Or Priority Queue Information Construction Inward Coffee Alongside Event - Tutorial
link : What Is Priorityqueue Or Priority Queue Information Construction Inward Coffee Alongside Event - Tutorial

What Is Priorityqueue Or Priority Queue Information Construction Inward Coffee Alongside Event - Tutorial

PriorityQueue is an unbounded Queue implementation inward Java, which is based on priority heap. PriorityQueue allows y'all to acquire out along elements inward a item order, according to at that spot natural gild or custom gild defined by Comparator interface inward Java. Head of priority queue information construction will ever incorporate to the lowest degree chemical constituent amongst honor to specified ordering. For example, inward this post, nosotros volition practise a PriorityQueue of Items, which are ordered based upon at that spot price, this volition allow us to procedure Items, starting from lowest price. Priority queue is equally good really useful inward implementing Dijkstra algorithm inward Java. You tin utilization to PriorityQueue to acquire out along unsettled nodes for processing. One of the key matter to recall most PriorityQueue inward Java is that it's Iterator doesn't guarantee whatsoever order, if y'all desire to traverse inward ordered fashion, meliorate utilization Arrays.sort(pq.toArray()) method. PriorityQueue is equally good not synchronized, which agency tin non live on shared safely betwixt multiple threads, instead it's concurrent counterpart PriorityBlockingQueue is thread-safe too should live on used inward multithreaded environment. Priority queue provides O(log(n)) fourth dimension functioning for mutual enqueing too dequeing methods e.g. offer(), poll() too add(), but constant fourth dimension for retrieval methods e.g. peek() too element().

How to utilization PriorityQueue inward Java

Comparator provided to PriorityQueue. In this example, nosotros get got kept break of Items inward PriorityQueue, whose natural ordering is decided past times it's price. 

You tin accept a hold off at Item course of report compareTo method, it's consistent with equals method and equally good sorts Items based upon at that spot price. I get got equally good practise Item equally nested static course of report here. By storing Item inward priority queue, y'all tin ever retrieve Item amongst lowest cost past times using poll() method of Queue interface.

package test;

import java.util.PriorityQueue;

import java.util.Queue;

/**

  * Java Program to present How to utilization PriorityQueue inward Java. This instance equally good demonstrate

  * that PriorityQueue doesn't allow goose egg elements too how PriorityQueue keeps elements i.e. ordering.

  *

  * @author

 */

public class PriorityQueueTest {

    public static void main(String args[]) {

        Queue<Item> items = new PriorityQueue<Item>();

        items.add(new Item("IPone", 900));

        items.add(new Item("IPad", 1200));

        items.add(new Item("Xbox", 300));

        items.add(new Item("Watch", 200));

        System.out.println("Order of items inward PriorityQueue");

        System.out.println(items);

      

        System.out.println("Element consumed from caput of the PriorityQueue : " + items.poll());

        System.out.println(items);

      

        System.out.println("Element consumed from caput of the PriorityQueue : " + items.poll());

        System.out.println(items);

      

        System.out.println("Element consumed from caput of the PriorityQueue : " + items.poll());

        System.out.println(items);

      

        //items.add(null); // goose egg elements non allowed inward PriorityQueue - NullPointerException

    }

    private static class Item implements Comparable<Item> {

        private String name;

        private int price;

        public Item(String name, int price) {

            this.name = name;

            this.price = price;

        }

        public String getName() {

            return name;

        }

        public int getPrice() {

            return price;

        }

        @Override

        public boolean equals(Object obj) {

            if (obj == null) {

                return false;

            }

            if (getClass() != obj.getClass()) {

                return false;

            }

            final Item other = (Item) obj;

            if ((this.name == null) ? (other.name != null) : !this.name.equals(other.name)) {

                return false;

            }

            if (this.price != other.price) {

                return false;

            }

            return true;

        }

        @Override

        public int hashCode() {

            int hash = 5;

            hash = 97  hash + (this.name != null ? this.name.hashCode() : 0);

            hash = 97  hash + this.price;

            return hash;

        }

        @Override

        public int compareTo(Item i) {

            if (this.price == i.price) {

                return this.name.compareTo(i.name);

            }

            return this.price - i.price;

        }

        @Override

        public String toString() {

            return String.format("%s: $%d", name, price);

        }      

      

    }

}

Output:

Order of items inward PriorityQueue

[Watch: $200, Xbox: $300, IPone: $900, IPad: $1200]

Element consumed from caput of the PriorityQueue : Watch: $200

[Xbox: $300, IPad: $1200, IPone: $900]

Element consumed from caput of the PriorityQueue : Xbox: $300

[IPone: $900, IPad: $1200]

Element consumed from caput of the PriorityQueue : IPone: $900

[IPad: $1200]

From the higher upwards output, it's clear that PriorityQueue keeps to the lowest degree value chemical constituent at head, where ordering is determined using compareTo() method. It doesn't acquire out along all elements inward that gild though, exclusively caput existence to the lowest degree value chemical constituent is guaranteed. This is inward fact primary departure betwixt TreeSet too PriorityQueue inward Java, old keeps all elements inward a item sorted order, land priority queue only keeps caput inward sorted order. Another of import betoken to banking concern complaint is that PriorityQueue  doesn't permit goose egg elements too trying to add together goose egg elements volition result inward NullPointerException, as shown below :

Exception inward thread "main" java.lang.NullPointerException

        at java.util.PriorityQueue.offer(PriorityQueue.java:265)

        at java.util.PriorityQueue.add(PriorityQueue.java:251)

        at test.PriorityQueueTest.main(PriorityQueueTest.java:36)

Java Result: 1

Summary

Like whatsoever other Collection class, it's worth noting to recall key points most PriorityQueue inward Java.

1) PriorityQueue is non synchronized, if thread-safety is requirement utilization BlockingPriorityQueue.

2) Queue retrieval methods similar poll(), peek() too element() access caput of Queue, which keeps to the lowest degree chemical constituent according to specified ordering.

3) Iterator returned past times PriorityQueue doesn't offering whatsoever ordering traversal guarantee.

4) PriorityQueue doesn't allow null elements, if y'all endeavour to add together null, it volition throw java.lang.NullPointerException.

That's all on what is PriorityQueue inward Java too How to utilization them. It's an particular class, which tin live on used inward particular scenarios, where y'all ask to eat Orders inward a item order, recall BlockingQueue maintains insertion order, but if desire to maintain a custom order, PriorityQueue or BlockingPriorityQueue is correct collection to use. TreeSet equally good provides similar functionality, but doesn't get got 1 brusque retrieval cum removal method e.g. poll().

Further Learning
Java In-Depth: Become a Complete Java Engineer
Java Fundamentals: Collections
Data Structures too Algorithms: Deep Dive Using Java

Recommended Book

Though PriorityQueue has quite specialized use, it is 1 of the Collection class, which is oft overlooked. Like whatsoever other Collection topic, Java Generics too Collection contains to a greater extent than or less of the best available information most PriorityQueue. If y'all similar to larn more, accept a re-create of that book.

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