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java.util.concurrent
Class PriorityBlockingQueue<E>
java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractQueue<E>
java.util.concurrent.PriorityBlockingQueue<E>
-
-
Type Parameters:
-
E - the type of elements held in this collection
-
All Implemented Interfaces:
-
Serializable
,
Iterable
<E>,
Collection
<E>,
BlockingQueue
<E>,
Queue
<E>
-
public 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>> {
final static 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
Java Collections Framework
.
-
Since:
-
1.5
-
See Also:
-
Serialized Form
Constructor Summary
|
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. |
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
natural ordering
of its elements. |
boolean |
contains
(
Object
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. |
|
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. |
PriorityBlockingQueue
public PriorityBlockingQueue()
-
Creates a
PriorityBlockingQueue
with the default initial capacity (11) that orders its elements according to their
natural ordering
.
PriorityBlockingQueue
public PriorityBlockingQueue(int initialCapacity)
-
Creates a
PriorityBlockingQueue
with the specified initial capacity that orders its elements according to their
natural ordering
.
-
Parameters:
-
initialCapacity - the initial capacity for this priority queue
-
Throws:
-
IllegalArgumentException
- if
initialCapacity
is less than 1
PriorityBlockingQueue
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,
null
then
the
natural ordering
of
order depends on
the
elements will be used.
elements' natural ordering.
-
Throws:
-
IllegalArgumentException
- if
initialCapacity
is less than 1
PriorityBlockingQueue
public PriorityBlockingQueue(Collection<? extends E> c)
-
Creates a
PriorityBlockingQueue
containing the elements in the specified collection.
The priority queue has an initial capacity of 110% of the size of the specified collection.
If the specified collection is a
SortedSet
or a
PriorityQueue
, this priority queue will be
ordered
sorted
according to the same
ordering.
comparator, or according to the natural ordering of its elements if the collection is sorted according to the natural ordering of its elements.
Otherwise, this priority queue
will be
is
ordered according to the
natural ordering
natural ordering
of its elements.
-
Parameters:
-
c - the collection whose elements are to be placed into this priority
queue
queue.
-
Throws:
-
ClassCastException
- if elements of the specified collection cannot be compared to one another according to the priority queue's
ordering
ordering.
-
NullPointerException
- if the specified collection or any of its elements are null
add
public boolean add(E e)
-
Inserts the specified element into this priority queue.
-
-
Specified by:
-
add
in interface
Collection
<
E
>
-
Specified by:
-
add
in interface
BlockingQueue
<
E
>
-
Specified by:
-
add
in interface
Queue
<
E
>
-
Overrides:
-
add
in class
AbstractQueue
<
E
>
-
-
Parameters:
-
e - the element to add
-
Returns:
-
true
(as specified by
Collection.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
offer
public boolean offer(E e)
-
Inserts the specified element into this priority queue.
-
-
Specified by:
-
offer
in interface
BlockingQueue
<
E
>
-
Specified by:
-
offer
in interface
Queue
<
E
>
-
-
Parameters:
-
e - the element to add
-
Returns:
-
true
(as specified by
Queue.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
put
public void put(E e)
-
Inserts the specified element into this priority queue. As the queue is unbounded this method will never block.
-
-
Specified by:
-
put
in interface
BlockingQueue
<
E
>
-
-
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
offer
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.
-
-
Specified by:
-
offer
in interface
BlockingQueue
<
E
>
-
-
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
-
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
poll
public E poll()
-
Description copied from interface:
Queue
-
Retrieves and removes the head of this queue, or returns
null
if this queue is empty.
-
-
Specified by:
-
poll
in interface
Queue
<
E
>
-
-
Returns:
-
the head of this queue, or
null
if this queue is empty
take
public 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.
-
-
Specified by:
-
take
in interface
BlockingQueue
<
E
>
-
-
Returns:
-
the head of this queue
-
Throws:
-
InterruptedException
- if interrupted while waiting
poll
public 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.
-
-
Specified by:
-
poll
in interface
BlockingQueue
<
E
>
-
-
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
- if interrupted while waiting
peek
public 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.
-
-
Specified by:
-
peek
in interface
Queue
<
E
>
-
-
Returns:
-
the head of this queue, or
null
if this queue is empty
comparator
public 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.
-
-
-
Returns:
-
the comparator used to order the elements in this queue, or
null
if this queue uses the natural ordering of its
elements
elements.
size
public 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
.
-
-
Specified by:
-
size
in interface
Collection
<
E
>
-
Specified by:
-
size
in class
AbstractCollection
<
E
>
-
-
Returns:
-
the number of elements in this collection
remainingCapacity
public int remainingCapacity()
-
Always returns
Integer.MAX_VALUE
because a
PriorityBlockingQueue
is not capacity constrained.
-
-
Specified by:
-
remainingCapacity
in interface
BlockingQueue
<
E
>
-
-
Returns:
-
Integer.MAX_VALUE
remove
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),
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).
-
-
Specified by:
-
remove
in interface
Collection
<
E
>
-
Specified by:
-
remove
in interface
BlockingQueue
<
E
>
-
Overrides:
-
remove
in class
AbstractCollection
<
E
>
-
-
Parameters:
-
o - element to be removed from this queue, if present
-
Returns:
-
true
if this queue changed as a result of the call
contains
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).
o.equals(e)
.
-
-
Specified by:
-
contains
in interface
Collection
<
E
>
-
Specified by:
-
contains
in interface
BlockingQueue
<
E
>
-
Overrides:
-
contains
in class
AbstractCollection
<
E
>
-
-
Parameters:
-
o - object to be checked for containment in this queue
-
Returns:
-
true
if this queue contains the specified element
toArray
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.
-
-
Specified by:
-
toArray
in interface
Collection
<
E
>
-
Overrides:
-
toArray
in class
AbstractCollection
<
E
>
-
-
Returns:
-
an array containing all of the elements in this queue
toString
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)
.
-
-
Overrides:
-
toString
in class
AbstractCollection
<
E
>
-
-
Returns:
-
a string representation of this collection
drainTo
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.
-
-
Specified by:
-
drainTo
in interface
BlockingQueue
<
E
>
-
-
Parameters:
-
c - the collection to transfer elements into
-
Returns:
-
the number of elements transferred
-
Throws:
-
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
drainTo
public 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.
-
-
Specified by:
-
drainTo
in interface
BlockingQueue
<
E
>
-
-
Parameters:
-
c - the collection to transfer elements into
-
maxElements - the maximum number of elements to transfer
-
Returns:
-
the number of elements transferred
-
Throws:
-
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
clear
public void clear()
-
Atomically removes all of the elements from this queue. The queue will be empty after this call returns.
-
-
Specified by:
-
clear
in interface
Collection
<
E
>
-
Overrides:
-
clear
in class
AbstractQueue
<
E
>
-
toArray
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()
.
-
-
Specified by:
-
toArray
in interface
Collection
<
E
>
-
Overrides:
-
toArray
in class
AbstractCollection
<
E
>
-
-
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
iterator
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
iterator
is a
"weakly consistent"
thread-safe "fast-fail"
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.
upon detected interference.
-
-
Specified by:
-
iterator
in interface
Iterable
<
E
>
-
Specified by:
-
iterator
in interface
Collection
<
E
>
-
Specified by:
-
iterator
in class
AbstractCollection
<
E
>
-
-
Returns:
-
an iterator over the elements in this queue