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 an element into a full queue
will result in the operation blocking; attempts to
take 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
../../../../technotes/guides/collections/index.html">
Java Collections Framework.
T[] toArray
public T[] toArray(T[] a)
Returns an array containing all of the elements in this queue, in
proper sequence; the runtime type of the returned array is that of
the specified array. 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().
- T[] toArray in interface Collection<E>
- T[] toArray in interface AbstractCollection<E>
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
- an array containing all of the elements in this queue
add
public boolean add(E e)
Inserts the specified element at the tail of this queue if it is
possible to do so immediately without exceeding the queue's capacity,
returning true upon success and throwing an
IllegalStateException if this queue is full.
- add in interface BlockingQueue<E>
- add in interface Queue<E>
- add in interface Collection<E>
- add in interface AbstractQueue<E>
iterator
public Iterator 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.
- iterator in interface Collection<E>
- iterator in interface Iterable<E>
- iterator in interface AbstractCollection<E>
- an iterator over the elements in this queue in proper sequence
offer
public boolean offer(E e)
Inserts the specified element at the tail of this queue if it is
possible to do so immediately without exceeding the queue's capacity,
returning
true upon success and
false if this queue
is full. This method is generally preferable to method
add(E)
,
which can fail to insert an element only by throwing an exception.
- offer in interface BlockingQueue<E>
- offer in interface Queue<E>
offer
public boolean offer(E e,
long timeout,
TimeUnit unit)
throws InterruptedException
Inserts the specified element at the tail of this queue, waiting
up to the specified wait time for space to become available if
the queue is full.
- offer in interface BlockingQueue<E>
remainingCapacity
public int remainingCapacity()
Returns the number of additional 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 insert
an element will succeed by inspecting
remainingCapacity
because it may be the case that another thread is about to
insert or remove an element.
- remainingCapacity in interface BlockingQueue<E>
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), if this queue contains one or more such
elements.
Returns true if this queue contained the specified element
(or equivalently, if this queue changed as a result of the call).
- remove in interface BlockingQueue<E>
- remove in interface Collection<E>
- remove in interface AbstractCollection<E>
o
- element to be removed from this queue, if present
- true if this queue changed as a result of the call
toArray
public Object[] toArray()
Returns an array containing all of the elements in this queue, in
proper sequence.
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.
- toArray in interface Collection<E>
- toArray in interface AbstractCollection<E>
- an array containing all of the elements in this queue