implements BlockingQueue<E> Serializable
An unbounded {@linkplain BlockingQueue 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 {@linkplain Comparable 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;
}
}
Public Constructor Summary
PriorityBlockingQueue()
Creates a
PriorityBlockingQueue with the default
initial capacity (11) that orders its elements according to
their {@linkplain Comparable natural ordering}. |
|
PriorityBlockingQueue(int initialCapacity)
Creates a
PriorityBlockingQueue with the specified
initial capacity that orders its elements according to their
{@linkplain Comparable 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. |
|
PriorityBlockingQueue(Collection<? extends E> c)
Creates a
PriorityBlockingQueue containing the elements
in the specified collection. |
Public Method Summary
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 {@linkplain Comparable
natural ordering} of its elements. |
boolean | |
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.
|
int |
drainTo(Collection<? super E> c)
Removes all 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 | |
E |
peek()
Retrieves, but does not remove, the head of this queue,
or returns
null if this queue is empty. |
E | |
E |
poll()
Retrieves and removes the head of this queue,
or returns
null if this queue is empty. |
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 | |
int |
size()
Returns the number of elements in this collection.
|
Spliterator<E> |
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.
|
<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.
|
Object[] |
toArray()
Returns an array containing all of the elements in this queue.
|
String |
toString()
Returns a string representation of this collection.
|
Inherited Method Summary
Public Constructors
public PriorityBlockingQueue ()
Creates a PriorityBlockingQueue
with the default
initial capacity (11) that orders its elements according to
their {@linkplain Comparable natural ordering}.
public PriorityBlockingQueue (int initialCapacity)
Creates a PriorityBlockingQueue
with the specified
initial capacity that orders its elements according to their
{@linkplain Comparable natural ordering}.
Parameters
initialCapacity | the initial capacity for this priority queue |
---|
Throws
IllegalArgumentException | if initialCapacity is less
than 1
|
---|
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. If null , the {@linkplain Comparable
natural ordering} of the elements will be used. |
Throws
IllegalArgumentException | if initialCapacity is less
than 1
|
---|
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
{@linkplain Comparable 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 |
Public Methods
public boolean add (E e)
Inserts the specified element into this priority queue.
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 |
public void clear ()
Atomically removes all of the elements from this queue. The queue will be empty after this call returns.
public Comparator<? super E> comparator ()
Returns the comparator used to order the elements in this queue,
or null
if this queue uses the {@linkplain Comparable
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
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)
.
Parameters
o | object to be checked for containment in this queue |
---|
Returns
true
if this queue contains the specified element
public 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. 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.
Parameters
c | the collection to transfer elements into |
---|---|
maxElements | the maximum number of elements to transfer |
Returns
- the number of elements transferred
public int drainTo (Collection<? super E> c)
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.
Parameters
c | the collection to transfer elements into |
---|
Returns
- the number of elements transferred
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.
Returns
- an iterator over the elements in this queue
public boolean offer (E e)
Inserts the specified element into this priority queue.
As the queue is unbounded, this method will never return false
.
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 |
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
.
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 |
public E peek ()
Retrieves, but does not remove, the head of this queue,
or returns null
if this queue is empty.
Returns
- the head of this queue, or
null
if this queue is empty
public 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.
Parameters
timeout | how long to wait before giving up, in units of
unit |
---|---|
unit | a TimeUnit determining how to interpret the
timeout parameter |
Returns
- the head of this queue, or
null
if the specified waiting time elapses before an element is available
Throws
InterruptedException |
---|
public E poll ()
Retrieves and removes the head of this queue,
or returns null
if this queue is empty.
Returns
- the head of this queue, or
null
if this queue is empty
public void put (E e)
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never block.
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 |
public int remainingCapacity ()
Always returns Integer.MAX_VALUE
because
a PriorityBlockingQueue
is not capacity constrained.
Returns
Integer.MAX_VALUE
always
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).
Parameters
o | element to be removed from this queue, if present |
---|
Returns
true
if this queue changed as a result of the call
public int size ()
Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
Returns
- the number of elements in this collection
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
.
Returns
- a
Spliterator
over the elements in this queue
public E take ()
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
Returns
- the head of this queue
Throws
InterruptedException |
---|
public 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()
.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 |
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.
Returns
- an array containing all of the elements in this queue
public String toString ()
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)
.
Returns
- a string representation of this collection