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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
implements
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())
.
This class is a member of the
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 (using
Comparable
). |
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 (using
Comparable
). |
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
o)
Adds the specified element to this queue. |
void |
clear
()
Atomically removes all of the elements from this
delay
queue. |
Comparator
<? super
E
> |
comparator
()
Returns the comparator used to order this collection, or
null
if this collection is sorted according to its elements natural ordering (using
Comparable
). |
boolean |
contains
(
Object
o)
Returns
true
if this collection contains the specified element. |
int |
drainTo
(
Collection
<? super
E
> c)
Removes all available elements from this queue and adds them into 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 into the given collection. |
Iterator
<
E
> |
iterator
()
Returns an iterator over the elements in this queue. |
boolean |
offer
(
E
o)
Inserts the specified element into this priority queue. |
boolean |
offer
(
E
o, long timeout,
TimeUnit
unit)
Inserts the specified element into this priority queue. |
E
|
peek
()
Retrieves, but does not remove, the head of this queue, returning
null
if this queue is empty. |
E
|
poll
()
Retrieves and removes the head of this queue, or
null
if this queue is empty. |
E
|
poll
(long timeout,
TimeUnit
unit)
Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements are present on this queue. |
void |
put
(
E
o)
Adds the specified element to 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,
collection,
if it is
present.
present (optional operation).
|
int |
size
()
Returns the number of elements in this collection. |
E
|
take
()
Retrieves and removes the head of this queue, waiting if no elements are present on this queue. |
Object
[] |
toArray
()
Returns an array containing all of the elements in this collection. |
|
toArray
(T[] a)
Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. |
String
|
toString
()
Returns a string representation of this collection. |
Methods inherited from class java.util.
AbstractQueue
|
addAll
,
element
,
remove
|
Methods inherited from class java.util.
AbstractCollection
|
containsAll
,
isEmpty
,
removeAll
,
retainAll
|
Methods inherited from class java.lang.
Object
|
clone
,
equals
,
finalize
,
getClass
,
hashCode
,
notify
,
notifyAll
,
wait
,
wait
,
wait
|
Methods inherited from interface java.util.
Queue
|
element
,
remove
|
PriorityBlockingQueue
public PriorityBlockingQueue()
-
Creates a
PriorityBlockingQueue
with the default initial capacity (11) that orders its elements according to their natural ordering (using
Comparable
).
PriorityBlockingQueue
public PriorityBlockingQueue(int initialCapacity)
-
Creates a
PriorityBlockingQueue
with the specified initial capacity that orders its elements according to their natural ordering (using
Comparable
).
-
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 used to order this priority queue. If
null
then the order depends on the 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 sorted according to the same comparator, or according to its elements' natural order if the collection is sorted according to its elements' natural order. Otherwise, this priority queue is ordered according to its elements' natural order.
-
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
c
or any element within it is
null
add
public boolean add(E o)
-
Adds the specified element to this queue.
-
-
Specified by:
-
add
in interface
Collection
<
E
>
-
Specified by:
-
add
in interface
BlockingQueue
<
E
>
-
Overrides:
-
add
in class
AbstractQueue
<
E
>
-
-
Parameters:
-
o - the element to add
-
Returns:
-
true
(as per the general contract of
Collection.add
).
-
Throws:
-
NullPointerException
- if the specified element is
null
.
-
ClassCastException
- if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering.
comparator
public Comparator<? super E> comparator()
-
Returns the comparator used to order this collection, or
null
if this collection is sorted according to its elements natural ordering (using
Comparable
).
-
-
-
Returns:
-
the comparator used to order this collection, or
null
if this collection is sorted according to its elements natural ordering.
offer
public boolean offer(E o)
-
Inserts the specified element into this priority queue.
-
-
Specified by:
-
offer
in interface
BlockingQueue
<
E
>
-
Specified by:
-
offer
in interface
Queue
<
E
>
-
-
Parameters:
-
o - the element to add
-
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
.
put
public void put(E o)
-
Adds the specified element to this priority queue. As the queue is unbounded this method will never block.
-
-
Specified by:
-
put
in interface
BlockingQueue
<
E
>
-
-
Parameters:
-
o - the element to add
-
Throws:
-
ClassCastException
- if the 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 o,
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:
-
o - 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 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
.
take
public E take()
throws InterruptedException
-
Description copied from interface:
BlockingQueue
-
Retrieves and removes the head of this queue, waiting if no elements are present on this queue.
-
-
Specified by:
-
take
in interface
BlockingQueue
<
E
>
-
-
Returns:
-
the head of this queue
-
Throws:
-
InterruptedException
- if interrupted while waiting.
poll
public E poll()
-
Description copied from interface:
Queue
-
Retrieves and removes the head of this queue, or
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.
poll
public E poll(long timeout,
TimeUnit unit)
throws InterruptedException
-
Description copied from interface:
BlockingQueue
-
Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements are present on this queue.
-
-
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 present.
-
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, returning
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.
size
public int size()
-
Description copied from class:
AbstractCollection
-
Returns the number of elements in this collection. If the 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.
Description copied from class:
AbstractCollection
-
Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element
e
such that
(o==null ? e==null : o.equals(e))
, if the collection contains one or more such elements. Returns
true
if the collection contained the specified element (or equivalently, if the collection changed as a result of the call).
This implementation iterates over the collection looking for the specified element. If it finds the element, it removes the element from the collection using the iterator's remove method.
Note that this implementation throws an
UnsupportedOperationException
if the iterator returned by this collection's iterator method does not implement the
remove
method and this collection contains the specified object.
-
-
Specified by:
-
remove
in interface
Collection
<
E
>
-
Overrides:
-
remove
in class
AbstractCollection
<
E
>
-
-
Parameters:
-
o - element to be removed from this collection, if present.
-
Returns:
-
true
if the collection contained the specified element.
contains
public boolean contains(Object o)
-
Description copied from class:
AbstractCollection
-
Returns
true
if this collection contains the specified element. More formally, returns
true
if and only if this collection contains at least one element
e
such that
(o==null ? e==null : o.equals(e))
.
This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.
-
-
Specified by:
-
contains
in interface
Collection
<
E
>
-
Overrides:
-
contains
in class
AbstractCollection
<
E
>
-
-
Parameters:
-
o - object to be checked for containment in this collection.
-
Returns:
-
true
if this collection contains the specified element.
toArray
public Object[] toArray()
-
Description copied from class:
AbstractCollection
-
Returns an array containing all of the elements in this collection. If the collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array will be "safe" in that no references to it are maintained by the collection. (In other words, this method must allocate a new array even if the collection is backed by an Array). The caller is thus free to modify the returned array.
This implementation allocates the array to be returned, and iterates over the elements in the collection, storing each object reference in the next consecutive element of the array, starting with element 0.
-
-
Specified by:
-
toArray
in interface
Collection
<
E
>
-
Overrides:
-
toArray
in class
AbstractCollection
<
E
>
-
-
Returns:
-
an array containing all of the elements in this collection.
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)
.
This implementation creates an empty string buffer, appends a left square bracket, and iterates over the collection appending the string representation of each element in turn. After appending each element except the last, the string
", "
is appended. Finally a right bracket is appended. A string is obtained from the string buffer, and returned.
-
-
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 into 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.
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 into 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.
clear
public void clear()
-
Atomically removes all of the elements from this
delay
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)
-
Description copied from class:
AbstractCollection
-
Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection 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 collection.
If the collection fits in the specified array with room to spare (i.e., the array has more elements than the collection), the element in the array immediately following the end of the collection is set to
null
. This is useful in determining the length of the collection
only
if the caller knows that the collection does not contain any
null
elements.)
If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
This implementation checks if the array is large enough to contain the collection; if not, it allocates a new array of the correct size and type (using reflection). Then, it iterates over the collection, storing each object reference in the next consecutive element of the array, starting with element 0. If the array is larger than the collection, a
null
is stored in the first location after the end of the collection.
-
-
Specified by:
-
toArray
in interface
Collection
<
E
>
-
Overrides:
-
toArray
in class
AbstractCollection
<
E
>
-
-
Parameters:
-
a - the array into which the elements of the collection 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 the elements of the collection.
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 is a thread-safe "fast-fail" iterator that will throw
ConcurrentModificationException
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.