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FlexDoc/Javadoc 2.0 Demo Java Doc |
Class PriorityQueue<E>
java.util.PriorityQueue<E>
Type Parameters:
E - the type of elements held in this queue
All Implemented Interfaces:
public class PriorityQueue<E>
An unbounded priority
queue based on a priority heap.
The elements of the priority queue are ordered according to their
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() and the Spliterator provided in method spliterator()
are 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.
Since:
1.5
Author:
Josh Bloch, Doug Lea
See Also:
Constructor Summary |
Creates a PriorityQueue with the default initial
capacity (11) that orders its elements according to their
natural ordering.
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Creates a PriorityQueue containing the elements in the
specified collection.
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Creates a PriorityQueue with the default initial capacity and
whose elements are ordered according to the specified comparator.
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Creates a PriorityQueue with the specified initial
capacity that orders its elements according to their
natural ordering.
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Creates a PriorityQueue with the specified initial capacity
that orders its elements according to the specified comparator.
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Creates a PriorityQueue containing the elements in the
specified priority queue.
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Creates a PriorityQueue containing the elements in the
specified sorted set.
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Method Summary |
boolean |
Inserts the specified element into this priority queue.
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void |
Removes all of the elements from this priority queue.
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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.
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boolean |
Returns true if this queue contains the specified element.
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void |
Performs the given action for each element of the Iterable
until all elements have been processed or the action throws an
exception.
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Returns an iterator over the elements in this queue.
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boolean |
Inserts the specified element into this priority queue.
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Retrieves, but does not remove, the head of this queue,
or returns null if this queue is empty.
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Retrieves and removes the head of this queue,
or returns null if this queue is empty.
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boolean |
Removes a single instance of the specified element from this queue,
if it is present.
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boolean |
Removes all of this collection's elements that are also contained in the
specified collection (optional operation).
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boolean |
Removes all of the elements of this collection that satisfy the given
predicate.
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boolean |
Retains only the elements in this collection that are contained in the
specified collection (optional operation).
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int |
Returns the number of elements in this collection.
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Returns an array containing all of the elements in this queue.
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Returns an array containing all of the elements in this queue; the
runtime type of the returned array is that of the specified array.
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Methods inherited from class java.lang. Object |
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Methods inherited from interface java.util. Collection |
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Creates a
PriorityQueue with the default initial
capacity (11) that orders its elements according to their
natural ordering.
public PriorityQueue |
(int initialCapacity) |
Creates a
PriorityQueue with the specified initial
capacity that orders its elements according to their
natural ordering.
Parameters:
initialCapacity - the initial capacity for this priority queue
Throws:
Creates a
PriorityQueue with the default initial capacity and
whose elements are ordered according to the specified comparator.
Parameters:
comparator - the comparator that will be used to order this
priority queue. If
null, the
natural ordering of the elements will be used.
Since:
1.8
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
comparator - the comparator that will be used to order this
priority queue. If
null, the
natural ordering of the elements will be used.
Throws:
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.
Parameters:
c - the collection whose elements are to be placed
into this priority queue
Throws:
ClassCastException - if elements of the specified collection
cannot be compared to one another according to the priority
queue's ordering
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 placed
into this priority queue
Throws:
ClassCastException - if elements of
c cannot be
compared to one another according to
c's
ordering
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 placed
into this priority queue
Throws:
ClassCastException - if elements of the specified sorted
set cannot be compared to one another according to the
sorted set's ordering
Inserts the specified element into this priority queue.
Specified by:
Overrides:
Parameters:
e - the element to add
Returns:
Throws:
ClassCastException - if the specified element cannot be
compared with elements currently in this priority queue
according to the priority queue's ordering
Inserts the specified element into this priority queue.
Specified by:
Parameters:
e - the element to add
Returns:
Throws:
ClassCastException - if the specified element cannot be
compared with elements currently in this priority queue
according to the priority queue's ordering
Description copied from interface:
Queue
Retrieves, but does not remove, the head of this queue,
or returns null if this queue is empty.
Specified by:
Returns:
the head of this queue, or null if this queue is empty
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).
Specified by:
Overrides:
Parameters:
o - element to be removed from this queue, if present
Returns:
true if this queue changed as a result of the call
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).
Specified by:
Overrides:
Parameters:
o - object to be checked for containment in this queue
Returns:
true if this queue contains the specified element
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.
Specified by:
Overrides:
Returns:
an array containing all of the elements in this queue
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().
Specified by:
Overrides:
Type Parameters:
T - the component type of the array to contain the collection
Parameters:
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.
Returns:
an array containing all of the elements in this queue
Throws:
ArrayStoreException - if the runtime type of the specified array
is not a supertype of the runtime type of every element in
this queue
Returns an iterator over the elements in this queue. The iterator
does not return the elements in any particular order.
Specified by:
Overrides:
Returns:
an iterator over the elements in this queue
Returns the number of elements in this collection. If this collection
contains more than Integer.MAX_VALUE elements, returns
Integer.MAX_VALUE.
Specified by:
Overrides:
Returns:
the number of elements in this collection
Removes all of the elements from this priority queue.
The queue will be empty after this call returns.
Specified by:
Overrides:
Description copied from interface:
Queue
Retrieves and removes the head of this queue,
or returns null if this queue is empty.
Specified by:
Returns:
the head of this queue, or null if this queue is empty
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.
Returns:
the comparator used to order this queue, or
null if this queue is sorted according to the
natural ordering of its elements
Creates a
late-binding
and
fail-fast Spliterator over the elements in this
queue. The spliterator does not traverse elements in any particular order
(the
ORDERED characteristic is not reported).
The Spliterator reports Spliterator.SIZED,
Spliterator.SUBSIZED, and Spliterator.NONNULL.
Overriding implementations should document the reporting of additional
characteristic values.
Specified by:
Returns:
a Spliterator over the elements in this queue
Since:
1.8
Removes all of the elements of this collection that satisfy the given
predicate. Errors or runtime exceptions thrown during iteration or by
the predicate are relayed to the caller.
Specified by:
Parameters:
filter - a predicate which returns true for elements to be
removed
Returns:
true if any elements were removed
Throws:
Removes all of this collection's elements that are also contained in the
specified collection (optional operation). After this call returns,
this collection will contain no elements in common with the specified
collection.
Specified by:
Overrides:
Parameters:
c - collection containing elements to be removed from this collection
Returns:
true if this collection changed as a result of the
call
Throws:
NullPointerException - if this collection contains one or more
null elements and the specified collection does not support
null elements
(
optional),
or if the specified collection is null
See Also:
Retains only the elements in this collection that are contained in the
specified collection (optional operation). In other words, removes from
this collection all of its elements that are not contained in the
specified collection.
Specified by:
Overrides:
Parameters:
c - collection containing elements to be retained in this collection
Returns:
true if this collection changed as a result of the call
Throws:
NullPointerException - if this collection contains one or more
null elements and the specified collection does not permit null
elements
(
optional),
or if the specified collection is null
See Also:
Description copied from interface:
Iterable
Performs the given action for each element of the
Iterable
until all elements have been processed or the action throws an
exception. Actions are performed in the order of iteration, if that
order is specified. Exceptions thrown by the action are relayed to the
caller.
The behavior of this method is unspecified if the action performs
side-effects that modify the underlying source of elements, unless an
overriding class has specified a concurrent modification policy.
Specified by:
Parameters:
action - The action to be performed for each element
Throws:
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