程序包 java.util

类 PriorityQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

java.util.PriorityQueue<E>

类型参数:

E - the type of elements held in this collection

所有已实现的接口:

Serializable, Iterable<E>, Collection<E>, Queue<E>

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

An unbounded priority Queue based on a priority heap. The elements of the priority queue are ordered according to their Comparable, 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.

从以下版本开始:

1.5

另请参阅:

序列化表格

构造器概要

构造器

构造器	说明
PriorityQueue()	Creates a PriorityQueue with the default initial capacity (11) that orders its elements according to their Comparable.
PriorityQueue(int initialCapacity)	Creates a PriorityQueue with the specified initial capacity that orders its elements according to their Comparable.
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(Comparator<? super E> comparator)	Creates a PriorityQueue with the default initial capacity and whose elements are ordered according to the specified comparator.
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.

方法概要

限定符和类型	方法	说明
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 Comparable 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()	Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
E	poll()	Retrieves and removes the head of this queue, or returns null if this queue is empty.
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.
Spliterator<E>	spliterator()	Creates a late-binding and fail-fast Spliterator over the elements in this queue.
Object[]	toArray()	Returns an array containing all of 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.

从类继承的方法 java.util.AbstractCollection

containsAll, isEmpty, removeAll, retainAll, toString

从类继承的方法 java.util.AbstractQueue

addAll, element, remove

从接口继承的方法 java.util.Collection

containsAll, equals, hashCode, isEmpty, parallelStream, removeAll, removeIf, retainAll, stream

从接口继承的方法 java.lang.Iterable

forEach

从类继承的方法 java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

构造器详细资料

PriorityQueue

public PriorityQueue()

Creates a PriorityQueue with the default initial capacity (11) that orders its elements according to their Comparable.

PriorityQueue

public PriorityQueue(int initialCapacity)

Creates a PriorityQueue with the specified initial capacity that orders its elements according to their Comparable.

参数:

initialCapacity - the initial capacity for this priority queue

抛出:

IllegalArgumentException - if initialCapacity is less than 1

PriorityQueue

public PriorityQueue(Comparator<? super E> comparator)

Creates a PriorityQueue with the default initial capacity and whose elements are ordered according to the specified comparator.

参数:

comparator - the comparator that will be used to order this priority queue. If null, the Comparable of the elements will be used.

从以下版本开始:

1.8

PriorityQueue

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

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

参数:

initialCapacity - the initial capacity for this priority queue

comparator - the comparator that will be used to order this priority queue. If null, the Comparable of the elements will be used.

抛出:

IllegalArgumentException - if initialCapacity is less than 1

PriorityQueue

public PriorityQueue(Collection<? extends E> c)

Creates a PriorityQueue containing the elements in the specified collection. If the specified collection is an instance of a SortedSet or is another PriorityQueue, this priority queue will be ordered according to the same ordering. Otherwise, this priority queue will be ordered according to the Comparable of its elements.

参数:

c - the collection whose elements are to be placed into this priority queue

抛出:

ClassCastException - if elements of the specified collection cannot be compared to one another according to the priority queue's ordering

NullPointerException - if the specified collection or any of its elements are null

PriorityQueue

public PriorityQueue(PriorityQueue<? extends E> c)

Creates a PriorityQueue containing the elements in the specified priority queue. This priority queue will be ordered according to the same ordering as the given priority queue.

参数:

c - the priority queue whose elements are to be placed into this priority queue

抛出:

ClassCastException - if elements of c cannot be compared to one another according to c's ordering

NullPointerException - if the specified priority queue or any of its elements are null

PriorityQueue

public PriorityQueue(SortedSet<? extends E> c)

Creates a PriorityQueue containing the elements in the specified sorted set. This priority queue will be ordered according to the same ordering as the given sorted set.

参数:

c - the sorted set whose elements are to be placed into this priority queue

抛出:

ClassCastException - if elements of the specified sorted set cannot be compared to one another according to the sorted set's ordering

NullPointerException - if the specified sorted set or any of its elements are null

方法详细资料

add

public boolean add(E e)

Inserts the specified element into this priority queue.

指定者:

add 在接口中 Collection<E>

指定者:

add 在接口中 Queue<E>

覆盖:

add 在类中 AbstractQueue<E>

参数:

e - the element to add

返回:

true (as specified by Collection#add)

抛出:

ClassCastException - if the specified element cannot be compared with elements currently in this priority queue according to the priority queue's ordering

NullPointerException - if the specified element is null

offer

public boolean offer(E e)

Inserts the specified element into this priority queue.

指定者:

offer 在接口中 Queue<E>

参数:

e - the element to add

返回:

true (as specified by Queue#offer)

抛出:

ClassCastException - if the specified element cannot be compared with elements currently in this priority queue according to the priority queue's ordering

NullPointerException - if the specified element is null

peek

public E peek()

从接口复制的说明: Queue

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

指定者:

peek 在接口中 Queue<E>

返回:

the head of this queue, or null if this queue is empty

remove

public boolean remove(Object o)

Removes a single instance of the specified element from this queue, if it is present. More formally, removes an element e such that o.equals(e), if this queue contains one or more such elements. Returns true if and only if this queue contained the specified element (or equivalently, if this queue changed as a result of the call).

指定者:

remove 在接口中 Collection<E>

覆盖:

remove 在类中 AbstractCollection<E>

参数:

o - element to be removed from this queue, if present

返回:

true if this queue changed as a result of the call

contains

public boolean contains(Object o)

Returns true if this queue contains the specified element. More formally, returns true if and only if this queue contains at least one element e such that o.equals(e).

指定者:

contains 在接口中 Collection<E>

覆盖:

contains 在类中 AbstractCollection<E>

参数:

o - object to be checked for containment in this queue

返回:

true if this queue contains the specified element

toArray

public Object[] toArray()

Returns an array containing all of the elements in this queue. The elements are in no particular order.

The returned array will be "safe" in that no references to it are maintained by this queue. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

指定者:

toArray 在接口中 Collection<E>

覆盖:

toArray 在类中 AbstractCollection<E>

返回:

an array containing all of the elements in this queue

toArray

public <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. The returned array elements are in no particular order. If the queue fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this queue.

If the queue fits in the specified array with room to spare (i.e., the array has more elements than the queue), the element in the array immediately following the end of the collection is set to null.

Like the toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

Suppose x is a queue known to contain only strings. The following code can be used to dump the queue into a newly allocated array of String:

 String[] y = x.toArray(new String[0]);

Note that toArray(new Object[0]) is identical in function to toArray().

指定者:

toArray 在接口中 Collection<E>

覆盖:

toArray 在类中 AbstractCollection<E>

类型参数:

T - the runtime type of the array to contain the collection

参数:

a - the array into which the elements of the queue are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

返回:

an array containing all of the elements in this queue

抛出:

ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue

NullPointerException - if the specified array is null

iterator

public Iterator<E> iterator()

Returns an iterator over the elements in this queue. The iterator does not return the elements in any particular order.

指定者:

iterator 在接口中 Collection<E>

指定者:

iterator 在接口中 Iterable<E>

指定者:

iterator 在类中 AbstractCollection<E>

返回:

an iterator over the elements in this queue

size

public int size()

从接口复制的说明: Collection

Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

指定者:

size 在接口中 Collection<E>

指定者:

size 在类中 AbstractCollection<E>

返回:

the number of elements in this collection

clear

public void clear()

Removes all of the elements from this priority queue. The queue will be empty after this call returns.

指定者:

clear 在接口中 Collection<E>

覆盖:

clear 在类中 AbstractQueue<E>

poll

public E poll()

从接口复制的说明: Queue

Retrieves and removes the head of this queue, or returns null if this queue is empty.

指定者:

poll 在接口中 Queue<E>

返回:

the head of this queue, or null if this queue is empty

comparator

public 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 Comparable of its elements.

返回:

the comparator used to order this queue, or null if this queue is sorted according to the natural ordering of its elements

spliterator

public final Spliterator<E> spliterator()

Creates a late-binding and fail-fast Spliterator over the elements in this queue.

The Spliterator reports Spliterator#SIZED, Spliterator#SUBSIZED, and Spliterator#NONNULL. Overriding implementations should document the reporting of additional characteristic values.

指定者:

spliterator 在接口中 Collection<E>

指定者:

spliterator 在接口中 Iterable<E>

返回:

a Spliterator over the elements in this queue

从以下版本开始:

1.8