PriorityQueue<E>
Java SE 6
| public class java.util PriorityQueue<E>
|
Java SE 6 |
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 java.util.concurrent.PriorityBlockingQueue class.
Implementation note: this implementation provides
O(log(n)) time for the enqueing and dequeing 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.
| since | 1.5 |
| version | 1.16, 04/21/06 |
| E | the type of elements held in this collection |
| Constructors | |||||||
|---|---|---|---|---|---|---|---|
| public | PriorityQueue() Creates a PriorityQueue with the default initial
capacity (11) that orders its elements according to their
natural ordering.
| ||||||
| public | PriorityQueue(int initialCapacity) Details
Creates a PriorityQueue with the specified initial
capacity that orders its elements according to their
natural ordering.
| ||||||
| public | PriorityQueue(int initialCapacity, Comparator comparator) Details
Creates a PriorityQueue with the specified initial capacity
that orders its elements according to the specified comparator.
| ||||||
| public | PriorityQueue(Collection c) Details
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
natural ordering of its elements.
| ||||||
| public | PriorityQueue(PriorityQueue c) Details
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.
| ||||||
| public | PriorityQueue(SortedSet c) Details
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.
| ||||||
| Methods | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| public boolean | add(Object e) Details
Inserts the specified element into this priority queue.
| ||||||||
| public void | clear() Removes all of the elements from this priority queue. The queue will be empty after this call returns. | ||||||||
| public Comparator | comparator() Details
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.
| ||||||||
| public boolean | contains(Object o) Details
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).
| ||||||||
| public Iterator | iterator() Details
Returns an iterator over the elements in this queue. The iterator
does not return the elements in any particular order.
| ||||||||
| public boolean | offer(Object e) Details
Inserts the specified element into this priority queue.
| ||||||||
| public Object | peek() | ||||||||
| public Object | poll() | ||||||||
| public boolean | remove(Object o) Details
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).
| ||||||||
| public int | size() | ||||||||
| public Object[] | toArray() Details
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.
| ||||||||
| public Object[]<T> | toArray(Object[] a) Details
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
Like the 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().
| ||||||||
| About DocWeb · Bundles · Export · Export All | Top 10 · Statistics · Login |
| About Sun · Contact · Privacy · Terms of Use · Trademarks | Java SE 6 · Copyright © 1994-2009 Sun Microsystems, Inc.All rights reserved. Use is subject to license terms |
 |
 |
|