java.util.concurrent.ArrayBlockingQueue<E>
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 offer an element to a full queue will
result in the 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 implements all of the optional methods
of the Collection and Iterator interfaces.
Summary
Public Constructors
Public Methods
add,
addAll,
clear,
contains,
containsAll,
isEmpty,
iterator,
remove,
removeAll,
retainAll,
size,
toArray,
toArray,
toString
clone,
equals,
finalize,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait
add,
addAll,
clear,
contains,
containsAll,
equals,
hashCode,
isEmpty,
iterator,
remove,
removeAll,
retainAll,
size,
toArray,
toArray
Methods inherited
from interface
java.util.Queue
Details
Public Constructors
public
ArrayBlockingQueue(int capacity)
Creates an
ArrayBlockingQueue with the given (fixed)
capacity and default access policy.
Parameters
capacity
| the capacity of this queue |
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. |
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 |
Public Methods
public
void
clear()
Removes all elements of the queue.
public
boolean
contains(Object o)
Searches this Collection for the specified object.
Parameters
o
| the object to search for |
Returns
- true if
object
is an element of this Collection,
false otherwise
public
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. 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.
public
int
drainTo(Collection<? super E> c)
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.
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.
Returns
- an iterator over the elements in this queue in proper sequence.
public
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.
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.
public
boolean
offer(E o)
Inserts the specified element at the tail of this queue if possible,
returning immediately if this queue is full.
Returns
- true if it was possible to add the element to
this queue, else false
public
E
peek()
Gets but not removes the element in the head of the queue, or throws
exception if there is no element in the queue.
public
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.
public
E
poll()
Gets and removes the element in the head of the queue, or returns null if
there is no element in the queue.
public
void
put(E o)
Adds the specified element to the tail of this queue, waiting if
necessary for space to become available.
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.
public
boolean
remove(Object o)
Removes the first occurrence of the specified object from this
Collection. This operation traverses over the collection, looking
for the specified object. Once the object is found, the object will
be removed from the collection using the iterator's remove method.
This collection will throw an UnsupportedOperationException if the
iterator returned does not implement remove method, and the specified
object is in this collection.
Returns
- true if this Collection is modified, false otherwise
public
int
size()
Returns the number of elements in this queue.
Returns
- the number of elements in this queue.
public
E
take()
Retrieves and removes the head of this queue, waiting
if no elements are present on this queue.
public
T[]
toArray(T[] a)
Returns an array containing all elements contained in this Collection. If
the specified array is large enough to hold the elements, the specified
array is used, otherwise an array of the same type is created. If the
specified array is used and is larger than this Collection, the array
element following the collection elements is set to null.
Returns
- an array of the elements from this Collection
public
Object[]
toArray()
Returns a new array containing all elements contained in this Collection.
All the elements in the array will not be referenced by the collection.
The elements in the returned array will be sorted to the same order as
those returned by the iterator of this collection itself if the collection
guarantees the order.
Returns
- an array of the elements from this Collection
public
String
toString()
Returns the string representation of this Collection. The presentation
has a specific format. It is enclosed by square brackets ("[]"). Elements
are separated by ', ' (comma and space).
Returns
- the string representation of this Collection