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FlexDoc/Javadoc 2.0 Demo Java Doc |
Class PriorityBlockingQueue<E>
java.util.concurrent.PriorityBlockingQueue<E>
Type Parameters:
E - the type of elements held in this queue
All Implemented Interfaces:
public class PriorityBlockingQueue<E>
An unbounded
blocking queue that uses
the same ordering rules as class
PriorityQueue and supplies
blocking retrieval operations. While this queue is logically
unbounded, attempted additions may fail due to resource exhaustion
(causing
OutOfMemoryError). This class does not permit
null elements. A priority queue relying on
natural ordering also does not permit insertion of
non-comparable objects (doing so results in
ClassCastException).
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 PriorityBlockingQueue in
any particular order. If you need ordered traversal, consider using
Arrays.sort(pq.toArray()). Also, method drainTo can
be used to remove some or all elements in priority order and
place them in another collection.
Operations on this class make no guarantees about the ordering
of elements with equal priority. If you need to enforce an
ordering, you can define custom classes or comparators that use a
secondary key to break ties in primary priority values. For
example, here is a class that applies first-in-first-out
tie-breaking to comparable elements. To use it, you would insert a
new FIFOEntry(anEntry) instead of a plain entry object.
class FIFOEntry<E extends Comparable<? super E>>
implements Comparable<FIFOEntry<E>> {
static final AtomicLong seq = new AtomicLong();
final long seqNum;
final E entry;
public FIFOEntry(E entry) {
seqNum = seq.getAndIncrement();
this.entry = entry;
}
public E getEntry() { return entry; }
public int compareTo(FIFOEntry<E> other) {
int res = entry.compareTo(other.entry);
if (res == 0 && other.entry != this.entry)
res = (seqNum < other.seqNum ? -1 : 1);
return res;
}
}
This class is a member of the
Java Collections Framework.
Since:
1.5
Author:
Doug Lea
See Also:
Constructor Summary |
Creates a PriorityBlockingQueue with the default
initial capacity (11) that orders its elements according to
their natural ordering.
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Creates a PriorityBlockingQueue containing the elements
in the specified collection.
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Creates a PriorityBlockingQueue with the specified
initial capacity that orders its elements according to their
natural ordering.
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Creates a PriorityBlockingQueue with the specified initial
capacity that orders its elements according to the specified
comparator.
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Method Summary |
boolean |
Inserts the specified element into this priority queue.
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void |
Atomically removes all of the elements from this queue.
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Returns the comparator used to order the elements in this queue,
or null if this queue uses the natural ordering of its elements.
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boolean |
Returns true if this queue contains the specified element.
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int |
Removes all available elements from this queue and adds them
to the given collection.
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int |
Removes at most the given number of available elements from
this queue and adds them to the given collection.
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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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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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Retrieves and removes the head of this queue, waiting up to the
specified wait time if necessary for an element to become available.
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void |
Inserts the specified element into this priority queue.
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int |
Always returns Integer.MAX_VALUE because
a PriorityBlockingQueue is not capacity constrained.
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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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Retrieves and removes the head of this queue, waiting if necessary
until an element becomes available.
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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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Returns a string representation of this collection.
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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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public PriorityBlockingQueue |
() |
Creates a
PriorityBlockingQueue with the default
initial capacity (11) that orders its elements according to
their
natural ordering.
public PriorityBlockingQueue |
(int initialCapacity) |
Creates a
PriorityBlockingQueue with the specified
initial capacity that orders its elements according to their
natural ordering.
Parameters:
initialCapacity - the initial capacity for this priority queue
Throws:
public PriorityBlockingQueue |
(int initialCapacity, Comparator<? super E> comparator) |
Creates a
PriorityBlockingQueue 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:
public PriorityBlockingQueue |
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Creates a
PriorityBlockingQueue containing the elements
in the specified collection. If the specified collection is a
SortedSet or a
PriorityBlockingQueue, 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
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 the priority queue according to the
priority queue's ordering
Inserts the specified element into this priority queue.
As the queue is unbounded, this method will never return
false.
Specified by:
Parameters:
e - the element to add
Returns:
Throws:
ClassCastException - if the specified element cannot be compared
with elements currently in the priority queue according to the
priority queue's ordering
Inserts the specified element into this priority queue.
As the queue is unbounded, this method will never block.
Specified by:
Parameters:
e - the element to add
Throws:
ClassCastException - if the specified element cannot be compared
with elements currently in the priority queue according to the
priority queue's ordering
Inserts the specified element into this priority queue.
As the queue is unbounded, this method will never block or
return
false.
Specified by:
Parameters:
e - the element to add
timeout - This parameter is ignored as the method never blocks
unit - This parameter is ignored as the method never blocks
Returns:
Throws:
ClassCastException - if the specified element cannot be compared
with elements currently in the priority queue according to the
priority queue's ordering
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
Retrieves and removes the head of this queue, waiting if necessary
until an element becomes available.
Specified by:
Returns:
the head of this queue
Throws:
Retrieves and removes the head of this queue, waiting up to the
specified wait time if necessary for an element to become available.
Specified by:
Parameters:
timeout - how long to wait before giving up, in units of
unit
unit - a TimeUnit determining how to interpret the
timeout parameter
Returns:
the head of this queue, or null if the
specified waiting time elapses before an element is available
Throws:
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
Returns the comparator used to order the elements in this queue,
or
null if this queue uses the
natural ordering of its elements.
Returns:
the comparator used to order the elements in this queue,
or null if this queue uses the natural
ordering of its elements
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
public int remainingCapacity |
() |
Always returns
Integer.MAX_VALUE because
a
PriorityBlockingQueue is not capacity constrained.
Specified by:
Returns:
Integer.MAX_VALUE always
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 a string representation of this collection. The string
representation consists of a list of the collection's elements in the
order they are returned by its iterator, enclosed in square brackets
(
"[]"). Adjacent elements are separated by the characters
", " (comma and space). Elements are converted to strings as
by
String.valueOf(Object).
Overrides:
Returns:
a string representation of this collection
Removes all available elements from this queue and adds them
to the given collection. This operation may be more
efficient than repeatedly polling this queue. A failure
encountered while attempting to add elements to
collection c may result in elements being in neither,
either or both collections when the associated exception is
thrown. Attempts to drain a queue to itself result in
IllegalArgumentException. Further, the behavior of
this operation is undefined if the specified collection is
modified while the operation is in progress.
Specified by:
Parameters:
c - the collection to transfer elements into
Returns:
the number of elements transferred
Throws:
UnsupportedOperationException - if addition of elements
is not supported by the specified collection
ClassCastException - if the class of an element of this queue
prevents it from being added to the specified collection
IllegalArgumentException - if the specified collection is this
queue, or some property of an element of this queue prevents
it from being added to the specified collection
Removes at most the given number of available elements from
this queue and adds them to the given collection. A failure
encountered while attempting to add elements to
collection c may result in elements being in neither,
either or both collections when the associated exception is
thrown. Attempts to drain a queue to itself result in
IllegalArgumentException. Further, the behavior of
this operation is undefined if the specified collection is
modified while the operation is in progress.
Specified by:
Parameters:
c - the collection to transfer elements into
maxElements - the maximum number of elements to transfer
Returns:
the number of elements transferred
Throws:
UnsupportedOperationException - if addition of elements
is not supported by the specified collection
ClassCastException - if the class of an element of this queue
prevents it from being added to the specified collection
IllegalArgumentException - if the specified collection is this
queue, or some property of an element of this queue prevents
it from being added to the specified collection
Atomically removes all of the elements from this queue.
The queue will be empty after this call returns.
Specified by:
Overrides:
Returns an array containing all of the elements in this queue.
The returned array 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 this queue fits in the specified array with room to spare
(i.e., the array has more elements than this queue), the element in
the array immediately following the end of the queue 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.
The returned iterator is
weakly consistent.
Specified by:
Overrides:
Returns:
an iterator over the elements in this queue
Returns a
Spliterator over the elements in this queue.
The spliterator does not traverse elements in any particular order
(the
ORDERED characteristic is not reported).
The returned spliterator is
weakly consistent.
The Spliterator reports Spliterator.SIZED and
Spliterator.NONNULL.
Implementation Note:
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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