E - the type of elements held in this queueSerializable, Iterable<E>, Collection<E>, BlockingQueue<E>, Queue<E>
public class PriorityBlockingQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, Serializable
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.
| Constructor | Description |
|---|---|
PriorityBlockingQueue() |
Creates a PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering. |
PriorityBlockingQueue |
Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to their natural ordering. |
PriorityBlockingQueue |
Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator. |
PriorityBlockingQueue |
Creates a PriorityBlockingQueue containing the elements in the specified collection. |
| Modifier and Type | Method | Description |
|---|---|---|
boolean |
add |
Inserts the specified element into this priority queue. |
void |
clear() |
Atomically removes all of the elements from this queue. |
Comparator |
comparator() |
Returns the comparator used to order the elements in this queue, or null if this queue uses the natural ordering of its elements. |
boolean |
contains |
Returns true if this queue contains the specified element. |
int |
drainTo |
Removes all available elements from this queue and adds them to the given collection. |
int |
drainTo |
Removes at most the given number of available elements from this queue and adds them to the given collection. |
void |
forEach |
Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. |
Iterator |
iterator() |
Returns an iterator over the elements in this queue. |
boolean |
offer |
Inserts the specified element into this priority queue. |
boolean |
offer |
Inserts the specified element into this priority queue. |
E |
peek() |
Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty. |
E |
poll() |
Retrieves and removes the head of this queue, or returns null if this queue is empty. |
E |
poll |
Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available. |
void |
put |
Inserts the specified element into this priority queue. |
int |
remainingCapacity() |
Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained. |
boolean |
remove |
Removes a single instance of the specified element from this queue, if it is present. |
boolean |
removeAll |
Removes all of this collection's elements that are also contained in the specified collection (optional operation). |
boolean |
removeIf |
Removes all of the elements of this collection that satisfy the given predicate. |
boolean |
retainAll |
Retains only the elements in this collection that are contained in the specified collection (optional operation). |
int |
size() |
Returns the number of elements in this collection. |
Spliterator |
spliterator() |
Returns a Spliterator over the elements in this queue. |
E |
take() |
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available. |
Object[] |
toArray() |
Returns an array containing all of the elements in this queue. |
<T> T[] |
toArray |
Returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array. |
addAll, element, remove
containsAll, isEmpty, toString
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
addAll, containsAll, equals, hashCode, isEmpty, parallelStream, stream, toArray
public PriorityBlockingQueue()
PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering.public PriorityBlockingQueue(int initialCapacity)
PriorityBlockingQueue with the specified initial capacity that orders its elements according to their natural ordering.initialCapacity - the initial capacity for this priority queueIllegalArgumentException - if initialCapacity is less than 1public PriorityBlockingQueue(int initialCapacity, Comparator<? super E> comparator)
PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator.initialCapacity - the initial capacity for this priority queuecomparator - the comparator that will be used to order this priority queue. If null, the natural ordering of the elements will be used.IllegalArgumentException - if initialCapacity is less than 1public PriorityBlockingQueue(Collection<? extends E> c)
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.c - the collection whose elements are to be placed into this priority queueClassCastException - if elements of the specified collection cannot be compared to one another according to the priority queue's orderingNullPointerException - if the specified collection or any of its elements are nullpublic boolean add(E e)
add in interface BlockingQueue<E>
add in interface Collection<E>
add in interface Queue<E>
add in class AbstractQueue<E>
e - the element to addtrue (as specified by Collection.add(E))ClassCastException - if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's orderingNullPointerException - if the specified element is nullpublic boolean offer(E e)
false.offer in interface BlockingQueue<E>
offer in interface Queue<E>
e - the element to addtrue (as specified by Queue.offer(E))ClassCastException - if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's orderingNullPointerException - if the specified element is nullpublic void put(E e)
put in interface BlockingQueue<E>
e - the element to addClassCastException - if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's orderingNullPointerException - if the specified element is nullpublic boolean offer(E e, long timeout, TimeUnit unit)
false.offer in interface BlockingQueue<E>
e - the element to addtimeout - This parameter is ignored as the method never blocksunit - This parameter is ignored as the method never blockstrue (as specified by BlockingQueue.offer)ClassCastException - if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's orderingNullPointerException - if the specified element is nullpublic E poll()
Queuenull if this queue is empty.public E take() throws InterruptedException
BlockingQueuetake in interface BlockingQueue<E>
InterruptedException - if interrupted while waitingpublic E poll(long timeout, TimeUnit unit) throws InterruptedException
BlockingQueuepoll in interface BlockingQueue<E>
timeout - how long to wait before giving up, in units of unit
unit - a TimeUnit determining how to interpret the timeout parameternull if the specified waiting time elapses before an element is availableInterruptedException - if interrupted while waitingpublic E peek()
Queuenull if this queue is empty.public Comparator<? super E> comparator()
null if this queue uses the natural ordering of its elements.null if this queue uses the natural ordering of its elementspublic int size()
CollectionInteger.MAX_VALUE elements, returns Integer.MAX_VALUE.size in interface Collection<E>
public int remainingCapacity()
Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.remainingCapacity in interface BlockingQueue<E>
Integer.MAX_VALUE alwayspublic boolean remove(Object o)
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).remove in interface BlockingQueue<E>
remove in interface Collection<E>
remove in class AbstractCollection<E>
o - element to be removed from this queue, if presenttrue if this queue changed as a result of the callpublic boolean contains(Object o)
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).contains in interface BlockingQueue<E>
contains in interface Collection<E>
contains in class AbstractCollection<E>
o - object to be checked for containment in this queuetrue if this queue contains the specified elementpublic int drainTo(Collection<? super E> c)
BlockingQueuec 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.drainTo in interface BlockingQueue<E>
c - the collection to transfer elements intoUnsupportedOperationException - if addition of elements is not supported by the specified collectionClassCastException - if the class of an element of this queue prevents it from being added to the specified collectionNullPointerException - if the specified collection is nullIllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collectionpublic int drainTo(Collection<? super E> c, int maxElements)
BlockingQueuec 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.drainTo in interface BlockingQueue<E>
c - the collection to transfer elements intomaxElements - the maximum number of elements to transferUnsupportedOperationException - if addition of elements is not supported by the specified collectionClassCastException - if the class of an element of this queue prevents it from being added to the specified collectionNullPointerException - if the specified collection is nullIllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collectionpublic void clear()
clear in interface Collection<E>
clear in class AbstractQueue<E>
public Object[] toArray()
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.
toArray in interface Collection<E>
toArray in class AbstractCollection<E>
public <T> T[] toArray(T[] a)
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().toArray in interface Collection<E>
toArray in class AbstractCollection<E>
T - the component type of the array to contain the collectiona - 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 purposeArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this queueNullPointerException - if the specified array is nullpublic Iterator<E> iterator()
The returned iterator is weakly consistent.
iterator in interface Collection<E>
iterator in interface Iterable<E>
iterator in class AbstractCollection<E>
public Spliterator<E> spliterator()
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.
spliterator in interface Collection<E>
spliterator in interface Iterable<E>
Spliterator additionally reports Spliterator.SUBSIZED.Spliterator over the elements in this queuepublic boolean removeIf(Predicate<? super E> filter)
CollectionremoveIf in interface Collection<E>
filter - a predicate which returns true for elements to be removedtrue if any elements were removedNullPointerException - if the specified filter is nullpublic boolean removeAll(Collection<?> c)
AbstractCollectionremoveAll in interface Collection<E>
removeAll in class AbstractCollection<E>
c - collection containing elements to be removed from this collectiontrue if this collection changed as a result of the callNullPointerException - 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 nullpublic boolean retainAll(Collection<?> c)
AbstractCollectionretainAll in interface Collection<E>
retainAll in class AbstractCollection<E>
c - collection containing elements to be retained in this collectiontrue if this collection changed as a result of the callNullPointerException - 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 nullpublic void forEach(Consumer<? super E> action)
IterableIterable 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.
forEach in interface Iterable<E>
action - The action to be performed for each elementNullPointerException - if the specified action is null
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/concurrent/PriorityBlockingQueue.html