E - the type of elements held in this collection
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() 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.
| Constructor and Description |
|---|
PriorityBlockingQueue()
Creates a
PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their
natural ordering.
|
PriorityBlockingQueue(Collection
Creates a
PriorityBlockingQueue containing the elements in the specified collection.
|
PriorityBlockingQueue(int initialCapacity)
Creates a
PriorityBlockingQueue with the specified initial capacity that orders its elements according to their
natural ordering.
|
PriorityBlockingQueue(int initialCapacity, Comparator
Creates a
PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator.
|
| Modifier and Type | Method and 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 |
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(Object
Returns
true if this queue contains the specified element.
|
int |
drainTo(Collection
Removes all available elements from this queue and adds them to the given collection.
|
int |
drainTo(Collection
Removes at most the given number of available elements from this queue and adds them to the given collection.
|
Iterator |
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
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(long timeout, TimeUnit
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(E e)
Inserts the specified element into this priority queue.
|
int |
remainingCapacity()
Always returns
Integer.MAX_VALUE because a
PriorityBlockingQueue is not capacity constrained.
|
boolean |
remove(Object
Removes a single instance of the specified element from this queue, if it is present.
|
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(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.
|
String |
toString()
Returns a string representation of this collection.
|
addAll, element, removecontainsAll, isEmpty, removeAll, retainAllclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitaddAll, containsAll, equals, hashCode, isEmpty, parallelStream, removeAll, removeIf, retainAll, streampublic 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 queue
IllegalArgumentException - if
initialCapacity is less than 1
public 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 queue
comparator - 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 1
public PriorityBlockingQueue(Collection<? extends E> c)
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 queue
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
public boolean add(E e)
add in interface
Collection<E>
add in interface
BlockingQueue<E>
add in interface
Queue<E>
add in class
AbstractQueue<E>
e - the element to add
true (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 ordering
NullPointerException - if the specified element is null
public boolean offer(E e)
false.
offer in interface
BlockingQueue<E>
offer in interface
Queue<E>
e - the element to add
true (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 ordering
NullPointerException - if the specified element is null
public void put(E e)
put in interface
BlockingQueue<E>
e - the element to add
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
public boolean offer(E e, long timeout, TimeUnitunit)
false.
offer in interface
BlockingQueue<E>
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
true (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 ordering
NullPointerException - if the specified element is null
public E poll()
Queue
null if this queue is empty.
public E take() throws InterruptedException
BlockingQueue
take in interface
BlockingQueue<E>
InterruptedException - if interrupted while waiting
public E poll(long timeout, TimeUnitunit) throws InterruptedException
BlockingQueue
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 parameter
null if the specified waiting time elapses before an element is available
InterruptedException - if interrupted while waiting
public E peek()
Queue
null 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 elements
public int size()
Collection
size in interface
Collection<E>
size in class
AbstractCollection<E>
public int remainingCapacity()
Integer.MAX_VALUE because a
PriorityBlockingQueue is not capacity constrained.
remainingCapacity in interface
BlockingQueue<E>
Integer.MAX_VALUE always
public boolean remove(Objecto)
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 present
true if this queue changed as a result of the call
public boolean contains(Objecto)
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 queue
true if this queue contains the specified element
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 StringtoString()
AbstractCollection
String.valueOf(Object) .
toString in class
AbstractCollection<E>
public int drainTo(Collection<? super E> c)
BlockingQueue
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 into
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
public int drainTo(Collection<? super E> c, int maxElements)
BlockingQueue
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 into
maxElements - the maximum number of elements to transfer
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
public void clear()
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 runtime type of the array to contain the collection
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
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
public Iterator<E> iterator()
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()
Spliterator over the elements in this queue.
The returned spliterator is weakly consistent.
The Spliterator reports Spliterator and Spliterator.
spliterator in interface
Iterable<E>
spliterator in interface
Collection<E>
Spliterator over the elements in this queue