Class PriorityBlockingQueue<E>
- java.lang.Object
-
- java.util.AbstractCollection<E>
-
- java.util.AbstractQueue<E>
-
- java.util.concurrent.PriorityBlockingQueue<E>
- Type Parameters:
-
E
- the type of elements held in this queue
- All Implemented Interfaces:
-
Serializable
,Iterable<E>
,Collection<E>
,BlockingQueue<E>
,Queue<E>
public class PriorityBlockingQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, Serializable
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(0); 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
- See Also:
- Serialized Form
Constructor Summary
Constructor | Description |
---|---|
PriorityBlockingQueue() | Creates a |
PriorityBlockingQueue(int initialCapacity) | Creates a |
PriorityBlockingQueue(int initialCapacity,
Comparator<? super E> comparator) | Creates a |
PriorityBlockingQueue(Collection<? extends E> c) | Creates a |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
boolean | add(E e) | Inserts the specified element into this priority queue. |
void | clear() | Atomically removes all of the elements from this queue. |
Comparator<? super E> | comparator() | Returns the comparator used to order the elements in this queue, or |
boolean | contains(Object o) | Returns |
int | drainTo(Collection<? super E> c) | Removes all available elements from this queue and adds them to the given collection. |
int | drainTo(Collection<? super E> c,
int maxElements) | Removes at most the given number of available elements from this queue and adds them to the given collection. |
void | forEach(Consumer<? super E> action) | Performs the given action for each element of the |
Iterator<E> | iterator() | Returns an iterator over the elements in this queue. |
boolean | offer(E e) | Inserts the specified element into this priority queue. |
boolean | offer(E e,
long timeout,
TimeUnit unit) | Inserts the specified element into this priority queue. |
void | put(E e) | Inserts the specified element into this priority queue. |
int | remainingCapacity() | Always returns |
boolean | remove(Object o) | Removes a single instance of the specified element from this queue, if it is present. |
boolean | removeAll(Collection<?> c) | Removes all of this collection's elements that are also contained in the specified collection (optional operation). |
boolean | removeIf(Predicate<? super E> filter) | Removes all of the elements of this collection that satisfy the given predicate. |
boolean | retainAll(Collection<?> c) | Retains only the elements in this collection that are contained in the specified collection (optional operation). |
Spliterator<E> | spliterator() | Returns a |
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. |
Methods declared in class java.util.AbstractQueue
addAll, element, remove
Methods declared in class java.util.AbstractCollection
containsAll, isEmpty, toString
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.concurrent.BlockingQueue
poll, take
Methods declared in interface java.util.Collection
addAll, containsAll, equals, hashCode, isEmpty, parallelStream, size, stream, toArray
Methods declared in interface java.util.Queue
element, peek, poll, remove
Constructor Detail
PriorityBlockingQueue
public PriorityBlockingQueue()
Creates a PriorityBlockingQueue
with the default initial capacity (11) that orders its elements according to their natural ordering.
PriorityBlockingQueue
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:
-
IllegalArgumentException
- ifinitialCapacity
is less than 1
PriorityBlockingQueue
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. Ifnull
, the natural ordering of the elements will be used. - Throws:
-
IllegalArgumentException
- ifinitialCapacity
is less than 1
PriorityBlockingQueue
public PriorityBlockingQueue(Collection<? extends E> c)
Creates a PriorityBlockingQueue
containing the elements in the specified collection. If the specified collection is a SortedSet
or a 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 -
NullPointerException
- if the specified collection or any of its elements are null
Method Detail
add
public boolean add(E e)
Inserts the specified element into this priority queue.
- Specified by:
-
add
in interfaceBlockingQueue<E>
- Specified by:
-
add
in interfaceCollection<E>
- Specified by:
-
add
in interfaceQueue<E>
- Overrides:
-
add
in classAbstractQueue<E>
- Parameters:
-
e
- the element to add - Returns:
-
true
(as specified byCollection.add(E)
) - Throws:
-
ClassCastException
- if the specified element cannot be compared with elements currently in the 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. As the queue is unbounded, this method will never return false
.
- Specified by:
-
offer
in interfaceBlockingQueue<E>
- Specified by:
-
offer
in interfaceQueue<E>
- Parameters:
-
e
- the element to add - Returns:
-
true
(as specified byQueue.offer(E)
) - Throws:
-
ClassCastException
- if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering -
NullPointerException
- if the specified element is null
put
public void put(E e)
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never block.
- Specified by:
-
put
in interfaceBlockingQueue<E>
- 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 -
NullPointerException
- if the specified element is null
offer
public boolean offer(E e, long timeout, TimeUnit unit)
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never block or return false
.
- Specified by:
-
offer
in interfaceBlockingQueue<E>
- 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:
-
true
(as specified byBlockingQueue.offer
) - Throws:
-
ClassCastException
- if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering -
NullPointerException
- if the specified element is null
comparator
public Comparator<? super E> comparator()
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
remainingCapacity
public int remainingCapacity()
Always returns Integer.MAX_VALUE
because a PriorityBlockingQueue
is not capacity constrained.
- Specified by:
-
remainingCapacity
in interfaceBlockingQueue<E>
- Returns:
-
Integer.MAX_VALUE
always
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).
- Specified by:
-
remove
in interfaceBlockingQueue<E>
- Specified by:
-
remove
in interfaceCollection<E>
- Overrides:
-
remove
in classAbstractCollection<E>
- Parameters:
-
o
- element to be removed from this queue, if present - Returns:
-
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)
.
- Specified by:
-
contains
in interfaceBlockingQueue<E>
- Specified by:
-
contains
in interfaceCollection<E>
- Overrides:
-
contains
in classAbstractCollection<E>
- Parameters:
-
o
- object to be checked for containment in this queue - Returns:
-
true
if this queue contains the specified element
drainTo
public int drainTo(Collection<? super E> c)
Description copied from interface: BlockingQueue
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:
-
drainTo
in interfaceBlockingQueue<E>
- 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 -
NullPointerException
- if the specified collection is null -
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
drainTo
public int drainTo(Collection<? super E> c, int maxElements)
Description copied from interface: BlockingQueue
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:
-
drainTo
in interfaceBlockingQueue<E>
- 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 -
NullPointerException
- if the specified collection is null -
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
clear
public void clear()
Atomically removes all of the elements from this queue. The queue will be empty after this call returns.
- Specified by:
-
clear
in interfaceCollection<E>
- Overrides:
-
clear
in classAbstractQueue<E>
toArray
public Object[] toArray()
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:
-
toArray
in interfaceCollection<E>
- Overrides:
-
toArray
in classAbstractCollection<E>
- Returns:
- 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 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:
-
toArray
in interfaceCollection<E>
- Overrides:
-
toArray
in classAbstractCollection<E>
- 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 -
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.
The returned iterator is weakly consistent.
- Specified by:
-
iterator
in interfaceCollection<E>
- Specified by:
-
iterator
in interfaceIterable<E>
- Specified by:
-
iterator
in classAbstractCollection<E>
- Returns:
- an iterator over the elements in this queue
spliterator
public Spliterator<E> spliterator()
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
.
- Specified by:
-
spliterator
in interfaceCollection<E>
- Specified by:
-
spliterator
in interfaceIterable<E>
- Implementation Note:
- The
Spliterator
additionally reportsSpliterator.SUBSIZED
. - Returns:
- a
Spliterator
over the elements in this queue - Since:
- 1.8
removeIf
public boolean removeIf(Predicate<? super E> filter)
Description copied from interface: Collection
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:
-
removeIf
in interfaceCollection<E>
- Parameters:
-
filter
- a predicate which returnstrue
for elements to be removed - Returns:
-
true
if any elements were removed - Throws:
-
NullPointerException
- if the specified filter is null
removeAll
public boolean removeAll(Collection<?> c)
Description copied from class: AbstractCollection
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:
-
removeAll
in interfaceCollection<E>
- Overrides:
-
removeAll
in classAbstractCollection<E>
- 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:
-
AbstractCollection.remove(Object)
,AbstractCollection.contains(Object)
retainAll
public boolean retainAll(Collection<?> c)
Description copied from class: AbstractCollection
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:
-
retainAll
in interfaceCollection<E>
- Overrides:
-
retainAll
in classAbstractCollection<E>
- 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:
-
AbstractCollection.remove(Object)
,AbstractCollection.contains(Object)
forEach
public void forEach(Consumer<? super E> action)
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:
-
forEach
in interfaceIterable<E>
- Parameters:
-
action
- The action to be performed for each element - Throws:
-
NullPointerException
- if the specified action is null