E - the type of elements held in this collectionpublic 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<? extends E> c)
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<? super E> 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<? 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. |
boolean |
contains(Object o)
Returns
true if this queue contains the specified element. |
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.
|
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.
|
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 unit)
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 o)
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.
|
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, removeAll, retainAllpublic 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 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)
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)
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()
Queuepublic 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
unitunit - a TimeUnit determining how to interpret the
timeout parameterInterruptedException - if interrupted while waitingpublic E peek()
Queuepublic 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()
Collectionsize 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 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 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)
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()
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()
AbstractCollectionString.valueOf(Object).toString in class AbstractCollection<E>public int drainTo(Collection<? super E> c)
BlockingQueuedrainTo 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)
BlockingQueuedrainTo 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 <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>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 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 a "weakly consistent" iterator that
will never throw ConcurrentModificationException, and guarantees to traverse
elements as they existed upon construction of the iterator, and
may (but is not guaranteed to) reflect any modifications
subsequent to construction.
iterator in interface Iterable<E>iterator in interface Collection<E>iterator in class AbstractCollection<E>