E - the type of elements held in this collectionpublic 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() is 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.
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.
initialCapacity - the initial capacity for this priority queueIllegalArgumentException - if initialCapacity is less than 1public PriorityBlockingQueue(int initialCapacity,
Comparator<? super E> comparator) Creates a 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)
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.
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)
Inserts the specified element into this priority queue.
add in interface Collection<E>
add in interface BlockingQueue<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)
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never return 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)
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never block.
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) Inserts the specified element into this priority queue. As the queue is unbounded, this method will never block or return 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()
Description copied from interface: Queue
Retrieves and removes the head of this queue, or returns null if this queue is empty.
poll in interface Queue<E>
null if this queue is emptypublic E take()
throws InterruptedException Description copied from interface: BlockingQueue
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
take in interface BlockingQueue<E>
InterruptedException - if interrupted while waitingpublic E poll(long timeout,
TimeUnit unit)
throws InterruptedException Description copied from interface: BlockingQueue
Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.
poll 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()
Description copied from interface: Queue
Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
peek in interface Queue<E>
null if this queue is emptypublic 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.
null if this queue uses the natural ordering of its elementspublic int size()
Description copied from interface: Collection
Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
size in interface Collection<E>
size in class AbstractCollection<E>
public int remainingCapacity()
Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.
remainingCapacity in interface BlockingQueue<E>
Integer.MAX_VALUE alwayspublic 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).
remove in interface Collection<E>
remove in interface BlockingQueue<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)
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).
contains in interface Collection<E>
contains in interface BlockingQueue<E>
contains in class AbstractCollection<E>
o - object to be checked for containment in this queuetrue if this queue contains the specified elementpublic 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.
toArray in interface Collection<E>
toArray in class AbstractCollection<E>
public String toString()
Description copied from class: AbstractCollection
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).
toString in class AbstractCollection<E>
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.
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) 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.
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()
Atomically removes all of the elements from this queue. The queue will be empty after this call returns.
clear in interface Collection<E>
clear in class AbstractQueue<E>
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().toArray in interface Collection<E>
toArray in class AbstractCollection<E>
T - the runtime 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()
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.
iterator in interface Iterable<E>
iterator in interface Collection<E>
iterator in class AbstractCollection<E>
public Spliterator<E> spliterator()
Returns a Spliterator over the elements in this queue.
The returned spliterator is weakly consistent.
The Spliterator reports Spliterator.SIZED and Spliterator.NONNULL.
spliterator in interface Iterable<E>
spliterator in interface Collection<E>
Spliterator additionally reports Spliterator.SUBSIZED.Spliterator over the elements in this queue
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