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java.util.concurrent
Class ArrayBlockingQueue<E>
java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractQueue<E>
java.util.concurrent.ArrayBlockingQueue<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 ArrayBlockingQueue<E>
- extends AbstractQueue<E>
- implements BlockingQueue<E>, Serializable
A bounded
blocking queue
backed by an array. This queue orders elements FIFO (first-in-first-out). The head of the queue is that element that has been on the queue the longest time. The tail of the queue is that element that has been on the queue the shortest time. New elements are inserted at the tail of the queue, and the queue retrieval operations obtain elements at the head of the queue.
This is a classic "bounded buffer", in which a fixed-sized array holds elements inserted by producers and extracted by consumers. Once created, the capacity cannot be increased. Attempts to
put
offer
an element to a full queue will result in the
put
offer
operation blocking; attempts to retrieve an element from an empty queue will similarly block.
This class supports an optional fairness policy for ordering waiting producer and consumer threads. By default, this ordering is not guaranteed. However, a queue constructed with fairness set to
true
grants threads access in FIFO order. Fairness generally decreases throughput but reduces variability and avoids starvation.
This class and its iterator implement all of the optional methods of the
Collection
and
Iterator
interfaces.
This class is a member of the
Java Collections Framework
.
-
Since:
-
1.5
-
See Also:
-
Serialized Form
Constructor Summary
|
ArrayBlockingQueue
(int capacity)
Creates an
ArrayBlockingQueue
with the given (fixed) capacity and default access policy. |
ArrayBlockingQueue
(int capacity, boolean fair)
Creates an
ArrayBlockingQueue
with the given (fixed) capacity and the specified access policy. |
ArrayBlockingQueue
(int capacity, boolean fair,
Collection
<? extends
E
> c)
Creates an
ArrayBlockingQueue
with the given (fixed) capacity, the specified access policy and initially containing the elements of the given collection, added in traversal order of the collection's iterator. |
Method Summary
|
void |
clear
()
Atomically removes
Removes
all of the elements from this
queue.
collection.
|
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 in proper sequence. |
boolean |
offer
(
E
o)
Inserts the specified element at the tail of this queue if possible, returning immediately if this queue is full. |
boolean |
offer
(
E
o, long timeout,
TimeUnit
unit)
Inserts the specified element at the tail of this queue, waiting if necessary up to the specified wait time for space to become available. |
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 the tail of this queue, waiting if necessary for space to become available. |
int |
remainingCapacity
()
Returns the number of elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking. |
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 queue. |
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
|
add
,
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
|
ArrayBlockingQueue
public ArrayBlockingQueue(int capacity)
-
Creates an
ArrayBlockingQueue
with the given (fixed) capacity and default access policy.
-
Parameters:
-
capacity - the capacity of this queue
-
Throws:
-
IllegalArgumentException
- if
capacity
is less than 1
ArrayBlockingQueue
public ArrayBlockingQueue(int capacity,
boolean fair)
-
Creates an
ArrayBlockingQueue
with the given (fixed) capacity and the specified access policy.
-
Parameters:
-
capacity - the capacity of this queue
-
fair - if
true
then queue accesses for threads blocked on insertion or removal, are processed in FIFO order; if
false
the access order is unspecified.
-
Throws:
-
IllegalArgumentException
- if
capacity
is less than 1
ArrayBlockingQueue
public ArrayBlockingQueue(int capacity,
boolean fair,
Collection<? extends E> c)
-
Creates an
ArrayBlockingQueue
with the given (fixed) capacity, the specified access policy and initially containing the elements of the given collection, added in traversal order of the collection's iterator.
-
Parameters:
-
capacity - the capacity of this queue
-
fair - if
true
then queue accesses for threads blocked on insertion or removal, are processed in FIFO order; if
false
the access order is unspecified.
-
c - the collection of elements to initially contain
-
Throws:
-
IllegalArgumentException
- if
capacity
is less than
c.size()
, or less than 1.
-
NullPointerException
- if
c
or any element within it is
null
offer
public boolean offer(E o)
-
Inserts the specified element at the tail of this queue if possible, returning immediately if this queue is full.
-
-
Specified by:
-
offer
in interface
BlockingQueue
<
E
>
-
Specified by:
-
offer
in interface
Queue
<
E
>
-
-
Parameters:
-
o - the element to add.
-
Returns:
-
true
if it was possible to add the element to this queue, else
false
-
Throws:
-
NullPointerException
- if the specified element is
null
offer
public boolean offer(E o,
long timeout,
TimeUnit unit)
throws InterruptedException
-
Inserts the specified element at the tail of this queue, waiting if necessary up to the specified wait time for space to become available.
-
-
Specified by:
-
offer
in interface
BlockingQueue
<
E
>
-
-
Parameters:
-
o - the element to add
-
timeout - how long to wait before giving up, in units of
unit
-
unit - a
TimeUnit
determining how to interpret the
timeout
parameter
-
Returns:
-
true
if successful, or
false
if the specified waiting time elapses before space is available.
-
Throws:
-
InterruptedException
- if interrupted while waiting.
-
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
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.
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.
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.
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.
put
public void put(E o)
throws InterruptedException
-
Adds the specified element to the tail of this queue, waiting if necessary for space to become available.
-
-
Specified by:
-
put
in interface
BlockingQueue
<
E
>
-
-
Parameters:
-
o - the element to add
-
Throws:
-
InterruptedException
- if interrupted while waiting.
-
NullPointerException
- if the specified element is
null
.
size
public int size()
-
Returns the number of elements in this queue.
-
-
Specified by:
-
size
in interface
Collection
<
E
>
-
Specified by:
-
size
in class
AbstractCollection
<
E
>
-
-
Returns:
-
the number of elements in this queue.
remainingCapacity
public int remainingCapacity()
-
Returns the number of elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking. This is always equal to the initial capacity of this queue less the current
size
of this queue.
Note that you cannot always tell if an attempt to
add
an element will succeed by inspecting
remainingCapacity
because it may be the case that a waiting consumer is ready to
take
an element out of an otherwise full queue.
-
-
Specified by:
-
remainingCapacity
in interface
BlockingQueue
<
E
>
-
-
Returns:
-
the remaining capacity
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.
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.
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.
clear
public void clear()
-
Atomically removes
Description copied from class:
AbstractQueue
-
Removes
all of the elements from this
queue.
collection.
The
queue
collection
will be empty after this call returns.
This implementation repeatedly invokes
poll
until it returns
null
.
-
-
Specified by:
-
clear
in interface
Collection
<
E
>
-
Overrides:
-
clear
in class
AbstractQueue
<
E
>
-
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.
iterator
public Iterator<E> iterator()
-
Returns an iterator over the elements in this queue in proper sequence. 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.
-
-
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 in proper sequence.