PriorityQueue

public class PriorityQueue extends AbstractQueue<E>
implements Serializable

An unbounded priority {@linkplain Queue queue} based on a priority heap. The elements of the priority queue are ordered according to their {@linkplain Comparable 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 (doing so may result in ClassCastException).

The head of this queue is the least element with respect to the specified ordering. If multiple elements are tied for least value, the head is one of those elements -- ties are broken arbitrarily. The queue retrieval operations poll, remove, peek, and element access the element at the head of the queue.

A priority queue is unbounded, but has an internal capacity governing the size of an array used to store the elements on the queue. It is always at least as large as the queue size. As elements are added to a priority queue, its capacity grows automatically. The details of the growth policy are not specified.

This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces. The Iterator provided in method iterator() is not guaranteed to traverse the elements of the priority queue in any particular order. If you need ordered traversal, consider using Arrays.sort(pq.toArray()).

Note that this implementation is not synchronized. Multiple threads should not access a PriorityQueue instance concurrently if any of the threads modifies the queue. Instead, use the thread-safe PriorityBlockingQueue class.

Implementation note: this implementation provides O(log(n)) time for the enqueuing and dequeuing methods (offer, poll, remove() and add); linear time for the remove(Object) and contains(Object) methods; and constant time for the retrieval methods (peek, element, and size).

This class is a member of the Java Collections Framework.

Public Constructor Summary

PriorityQueue()
Creates a PriorityQueue with the default initial capacity (11) that orders its elements according to their {@linkplain Comparable natural ordering}.
PriorityQueue(int initialCapacity)
Creates a PriorityQueue with the specified initial capacity that orders its elements according to their {@linkplain Comparable natural ordering}.
PriorityQueue(Comparator<? super E> comparator)
Creates a PriorityQueue with the default initial capacity and whose elements are ordered according to the specified comparator.
PriorityQueue(int initialCapacity, Comparator<? super E> comparator)
Creates a PriorityQueue with the specified initial capacity that orders its elements according to the specified comparator.
PriorityQueue(Collection<? extends E> c)
Creates a PriorityQueue containing the elements in the specified collection.
PriorityQueue(PriorityQueue<? extends E> c)
Creates a PriorityQueue containing the elements in the specified priority queue.
PriorityQueue(SortedSet<? extends E> c)
Creates a PriorityQueue containing the elements in the specified sorted set.

Public Method Summary

boolean
add(E e)
Inserts the specified element into this priority queue.
void
clear()
Removes all of the elements from this priority queue.
Comparator<? super E>
comparator()
Returns the comparator used to order the elements in this queue, or null if this queue is sorted according to the {@linkplain Comparable natural ordering} of its elements.
boolean
contains(Object o)
Returns true if this queue contains the specified element.
Iterator<E>
iterator()
Returns an iterator over the elements in this queue.
boolean
offer(E e)
Inserts the specified element into this priority queue.
E
peek()
E
poll()
boolean
remove(Object o)
Removes a single instance of the specified element from this queue, if it is present.
int
size()
Returns the number of elements in this collection.
final Spliterator<E>
spliterator()
Creates a late-binding and fail-fast Spliterator over the elements in this queue.
<T> T[]
toArray(T[] a)
Returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array.
Object[]
toArray()
Returns an array containing all of the elements in this queue.

Inherited Method Summary