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Showing content from https://www.tutorialspoint.com/java/util/java_util_priorityqueue.htm below:

Java PriorityQueue Class

Java PriorityQueue Class Introduction

The Java PriorityQueue class is an unbounded priority queue based on a priority heap. Following are the important points about PriorityQueue −

The elements of the priority queue are ordered according to their natural ordering, or by a Comparator provided at queue construction time, depending on which constructor is used.
A priority queue does not permit null elements.
A priority queue relying on natural ordering also does not permit insertion of non-comparable objects.

Class declaration

Following is the declaration for java.util.PriorityQueue class −

public class PriorityQueue<E>
   extends AbstractQueue<E>
   implements Serializable

Parameters

Following is the parameter for java.util.PriorityQueue class −

E − This is the type of elements held in this collection.

Class constructors Sr.No. Constructor & Description 1

PriorityQueue()

This creates a PriorityQueue with the default initial capacity (11) that orders its elements according to their natural ordering.

PriorityQueue(Collection<? extends E> c)

This creates a PriorityQueue containing the elements in the specified collection.

PriorityQueue(int initialCapacity)

This creates a PriorityQueue with the specified initial capacity that orders its elements according to their natural ordering.

PriorityQueue(int initialCapacity, Comparator<? super E> comparator)

This creates a PriorityQueue with the specified initial capacity that orders its elements according to the specified comparator.

PriorityQueue(PriorityQueue<? extends E> c)

This creates a PriorityQueue containing the elements in the specified priority queue.

PriorityQueue(SortedSet<? extends E> c)

This creates a PriorityQueue containing the elements in the specified sorted set.

Class methods Methods inherited

This class inherits methods from the following classes −

java.util.AbstractQueue
java.util.AbstractCollection
java.util.Object
java.util.Collection

Adding an Item to a Priority Queue Example

The following example shows the usage of Java PriorityQueue add(E) method to add Integers. We're adding couple of Integers to the PriorityQueue object using add() method calls per element and then print each element to show the elements added.

package com.tutorialspoint;

import java.util.PriorityQueue;

public class PriorityQueueDemo {
   public static void main(String[] args) {
      
      // create an empty priority queue with an initial capacity
      PriorityQueue<Integer> queue = new PriorityQueue<>(5);

      // use add() method to add elements in the queue
      queue.add(20);
      queue.add(30);
      queue.add(20);
      queue.add(30);
      queue.add(15);
      queue.add(22);
      queue.add(11);

      // let us print all the elements available in queue
      for (Integer number : queue) {
         System.out.println("Number = " + number);
      }
   }
}

Let us compile and run the above program, this will produce the following result −

Number = 11
Number = 20
Number = 15
Number = 30
Number = 30
Number = 22
Number = 20

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