public class

PriorityQueue

extends AbstractQueue<E>
java.lang.Object
   ↳ java.util.AbstractCollection<E>
     ↳ java.util.AbstractQueue<E>
       ↳ java.util.PriorityQueue<E>

Class Overview

A PriorityQueue holds elements on a priority heap, which orders the elements according to their natural order or according to the comparator specified at construction time. If the queue uses natural ordering, only elements that are comparable are permitted to be inserted into the queue.

The least element of the specified ordering is stored at the head of the queue and the greatest element is stored at the tail of the queue.

A PriorityQueue is not synchronized.

Summary

Public Constructors
PriorityQueue()
Constructs a priority queue with an initial capacity of 11 and natural ordering.
PriorityQueue(int initialCapacity)
Constructs a priority queue with the specified capacity and natural ordering.
PriorityQueue(int initialCapacity, Comparator<? super E> comparator)
Constructs a priority queue with the specified capacity and comparator.
PriorityQueue(Collection<? extends E> c)
Constructs a priority queue that contains the elements of a collection.
PriorityQueue(PriorityQueue<? extends E> c)
Constructs a priority queue that contains the elements of another priority queue.
PriorityQueue(SortedSet<? extends E> c)
Constructs a priority queue that contains the elements of a sorted set.
Public Methods
boolean add(Object o)
Adds the specified object to the priority queue.
void clear()
Removes all the elements of the priority queue.
Comparator<? super E> comparator()
Gets the comparator of the priority queue.
boolean contains(Object object)
Answers if there is an element in this queue equals to the object.
Iterator<E> iterator()
Gets the iterator of the priority queue, which will not return elements in any specified ordering.
boolean offer(Object o)
Inserts the element to the priority queue.
E peek()
Gets but does not remove the head of the queue.
E poll()
Gets and removes the head of the queue.
boolean remove(Object o)
Removes the specified object from the priority queue.
int size()
Gets the size of the priority queue.
Object[] toArray()
Returns all the elements in an array.
[Expand]
Inherited Methods
From class java.util.AbstractQueue
From class java.util.AbstractCollection
From class java.lang.Object
From interface java.lang.Iterable
From interface java.util.Collection
From interface java.util.Queue

Public Constructors

public PriorityQueue ()

Constructs a priority queue with an initial capacity of 11 and natural ordering.

public PriorityQueue (int initialCapacity)

Constructs a priority queue with the specified capacity and natural ordering.

Parameters
initialCapacity the specified capacity.
Throws
IllegalArgumentException if the initialCapacity is less than 1.

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

Constructs a priority queue with the specified capacity and comparator.

Parameters
initialCapacity the specified capacity.
comparator the specified comparator. If it is null, the natural ordering will be used.
Throws
IllegalArgumentException if the initialCapacity is less than 1.

public PriorityQueue (Collection<? extends E> c)

Constructs a priority queue that contains the elements of a collection. The constructed priority queue has the initial capacity of 110% of the size of the collection. The queue uses natural ordering to order its elements.

Parameters
c the collection whose elements will be added to the priority queue to be constructed.
Throws
ClassCastException if any of the elements in the collection are not comparable.
NullPointerException if any of the elements in the collection are null.

public PriorityQueue (PriorityQueue<? extends E> c)

Constructs a priority queue that contains the elements of another priority queue. The constructed priority queue has the initial capacity of 110% of the specified one. Both priority queues have the same comparator.

Parameters
c the priority queue whose elements will be added to the priority queue to be constructed.

public PriorityQueue (SortedSet<? extends E> c)

Constructs a priority queue that contains the elements of a sorted set. The constructed priority queue has the initial capacity of 110% of the size of the sorted set. The priority queue will have the same comparator as the sorted set.

Parameters
c the sorted set whose elements will be added to the priority queue to be constructed.

Public Methods

public boolean add (Object o)

Adds the specified object to the priority queue.

Parameters
o the object to be added.
Returns
  • always true.
Throws
ClassCastException if the element cannot be compared with the elements in the priority queue using the ordering of the priority queue.
NullPointerException if o is null.

public void clear ()

Removes all the elements of the priority queue.

public Comparator<? super E> comparator ()

Gets the comparator of the priority queue.

Returns
  • the comparator of the priority queue or null if the natural ordering is used.

public boolean contains (Object object)

Answers if there is an element in this queue equals to the object.

Parameters
object the object to search for.
Returns
  • true if object is an element of this Collection, false otherwise.
See Also

public Iterator<E> iterator ()

Gets the iterator of the priority queue, which will not return elements in any specified ordering.

Returns
  • the iterator of the priority queue.

public boolean offer (Object o)

Inserts the element to the priority queue.

Parameters
o the element to add to the priority queue.
Returns
  • always true
Throws
ClassCastException if the element cannot be compared with the elements in the priority queue using the ordering of the priority queue.
NullPointerException if o is null.

public E peek ()

Gets but does not remove the head of the queue.

Returns
  • the head of the queue or null if the queue is empty.

public E poll ()

Gets and removes the head of the queue.

Returns
  • the head of the queue or null if the queue is empty.

public boolean remove (Object o)

Removes the specified object from the priority queue.

Parameters
o the object to be removed.
Returns
  • true if the object was in the priority queue, false if the object was not in the priority queue.

public int size ()

Gets the size of the priority queue. If the size of the queue is greater than the Integer.MAX, then it returns Integer.MAX.

Returns
  • the size of the priority queue.

public Object[] toArray ()

Returns all the elements in an array. The result is a copy of all the elements.

Returns
  • the Array of all the elements
See Also