Java.util.PriorityQueue Class


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Introduction

The java.util.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

S.N. Constructor & Description
1

PriorityQueue()

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

2

PriorityQueue(Collection<? extends E> c)

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

3

PriorityQueue(int initialCapacity)

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

4

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.

5

PriorityQueue(PriorityQueue<? extends E> c)

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

6

PriorityQueue(SortedSet<? extends E> c)

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

Class methods

S.N. Method & Description
1

boolean add(E e)

This method inserts the specified element into this priority queue.

2

void clear()

This method removes all of the elements from this priority queue.

3

Comparator<? super E> comparator()

This method returns the comparator used to order the elements in this queue, or null if this queue is sorted according to the natural ordering of its elements.

4

boolean contains(Object o)

This method returns true if this queue contains the specified element.

5

Iterator<E> iterator()

This method returns an iterator over the elements in this queue.

6

boolean offer(E e)

This method inserts the specified element into this priority queue.

7

E peek()

This method retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.

8

E poll()

This method retrieves and removes the head of this queue, or returns null if this queue is empty.

9

boolean remove(Object o)

This method removes a single instance of the specified element from this queue, if it is present.

10

int size()

This method returns the number of elements in this collection.

11

Object[] toArray()

This method returns an array containing all of the elements in this queue.

12

<T> T[] toArray(T[] a)

This method returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array.

Methods inherited

This class inherits methods from the following classes:

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


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