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| java.util.PriorityQueue
| PriorityQueue | | public class PriorityQueue extends AbstractQueue implements java.io.Serializable(Code) | | An unbounded priority
based on a priority heap.
The elements of the priority queue are ordered according to their
, 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
PriorityQueue.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:
1.22, 05/05/07
author:
Josh Bloch, Doug Lea<
Parameters:
E - > the type of elements held in this collection |
| Constructor Summary | |
| public | PriorityQueue()
Creates a
PriorityQueue with the default initial
capacity (11) that orders its elements according to their
. | | public | PriorityQueue(int initialCapacity)
Creates a
PriorityQueue with the specified initial
capacity that orders its elements according to their
. | | 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.
Parameters:
initialCapacity - the initial capacity for this priority queue
Parameters:
comparator - the comparator that will be used to order thispriority queue. | | public | PriorityQueue(Collection<? extends E> c)
Creates a
PriorityQueue containing the elements in the
specified collection. | | public | PriorityQueue(PriorityQueue<? extends E> c)
Creates a
PriorityQueue containing the elements in the
specified priority queue. | | public | PriorityQueue(SortedSet<? extends E> c)
Creates a
PriorityQueue containing the elements in the
specified sorted set. |
| Method Summary | |
| public boolean | add(E e)
Inserts the specified element into this priority queue. | | public void | clear()
Removes all of the elements from this priority queue. | | 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
of its elements. | | public boolean | contains(Object o)
Returns
true if this queue contains the specified element. | | public Iterator<E> | iterator()
Returns an iterator over the elements in this queue. | | public boolean | offer(E e)
Inserts the specified element into this priority queue. | | public E | peek()
| | public E | poll()
| | public boolean | remove(Object o)
Removes a single instance of the specified element from this queue,
if it is present. | | boolean | removeEq(Object o)
Version of remove using reference equality, not equals. | | public int | size()
| | 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. | | public 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
PriorityQueue.toArray() method, this method acts as bridge between
array-based and collection-based APIs. |
| PriorityQueue | | public PriorityQueue()(Code) | | Creates a
PriorityQueue with the default initial
capacity (11) that orders its elements according to their
.
|
| PriorityQueue | | public PriorityQueue(int initialCapacity)(Code) | | Creates a
PriorityQueue with the specified initial
capacity that orders its elements according to their
.
Parameters:
initialCapacity - the initial capacity for this priority queue
throws:
IllegalArgumentException - if initialCapacity is lessthan 1 |
| PriorityQueue | | public PriorityQueue(int initialCapacity, Comparator<? super E> comparator)(Code) | | Creates a
PriorityQueue with the specified initial capacity
that orders its elements according to the specified comparator.
Parameters:
initialCapacity - the initial capacity for this priority queue
Parameters:
comparator - the comparator that will be used to order thispriority queue. If null , the of the elements will be used.
throws:
IllegalArgumentException - if initialCapacity isless than 1 |
| PriorityQueue | | public PriorityQueue(Collection<? extends E> c)(Code) | | 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
of its elements.
Parameters:
c - the collection whose elements are to be placedinto this priority queue
throws:
ClassCastException - if elements of the specified collectioncannot be compared to one another according to the priorityqueue's ordering
throws:
NullPointerException - if the specified collection or anyof its elements are null |
| PriorityQueue | | public PriorityQueue(PriorityQueue<? extends E> c)(Code) | | 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.
Parameters:
c - the priority queue whose elements are to be placedinto this priority queue
throws:
ClassCastException - if elements of c cannot becompared to one another according to c 'sordering
throws:
NullPointerException - if the specified priority queue or anyof its elements are null |
| PriorityQueue | | public PriorityQueue(SortedSet<? extends E> c)(Code) | | 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.
Parameters:
c - the sorted set whose elements are to be placedinto this priority queue
throws:
ClassCastException - if elements of the specified sortedset cannot be compared to one another according to thesorted set's ordering
throws:
NullPointerException - if the specified sorted set or anyof its elements are null |
| add | | public boolean add(E e)(Code) | | Inserts the specified element into this priority queue.
true (as specified by Collection.add)
throws:
ClassCastException - if the specified element cannot becompared with elements currently in this priority queueaccording to the priority queue's ordering
throws:
NullPointerException - if the specified element is null |
| clear | | public void clear()(Code) | | Removes all of the elements from this priority queue.
The queue will be empty after this call returns.
|
| comparator | | public Comparator<? super E> comparator()(Code) | | Returns the comparator used to order the elements in this
queue, or
null if this queue is sorted according to
the
of its elements.
the comparator used to order this queue, or null if this queue is sorted according to thenatural ordering of its elements |
| contains | | public boolean contains(Object o)(Code) | | 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) .
Parameters:
o - object to be checked for containment in this queue true if this queue contains the specified element |
| iterator | | public Iterator<E> iterator()(Code) | | Returns an iterator over the elements in this queue. The iterator
does not return the elements in any particular order.
an iterator over the elements in this queue |
| offer | | public boolean offer(E e)(Code) | | Inserts the specified element into this priority queue.
true (as specified by Queue.offer)
throws:
ClassCastException - if the specified element cannot becompared with elements currently in this priority queueaccording to the priority queue's ordering
throws:
NullPointerException - if the specified element is null |
| remove | | public boolean remove(Object o)(Code) | | 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).
Parameters:
o - element to be removed from this queue, if present true if this queue changed as a result of the call |
| removeEq | | boolean removeEq(Object o)(Code) | | Version of remove using reference equality, not equals.
Needed by iterator.remove.
Parameters:
o - element to be removed from this queue, if present true if removed |
| toArray | | public Object[] toArray()(Code) | | 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.
an array containing all of the elements in this queue |
| toArray | | public T[] toArray(T[] a)(Code) | | 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
PriorityQueue.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().
Parameters:
a - the array into which the elements of the queue are tobe stored, if it is big enough; otherwise, a new array of thesame runtime type is allocated for this purpose. an array containing all of the elements in this queue
throws:
ArrayStoreException - if the runtime type of the specified arrayis not a supertype of the runtime type of every element inthis queue
throws:
NullPointerException - if the specified array is null |
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