E - the type of elements held in this collectionpublic class ArrayBlockingDroppingQueue<E> extends AbstractQueue<E> implements BlockingDroppingQueue<E>, Serializable
Elements in the queue are ordered as 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 "ring 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 oldest item being removed to make room; attempts to take an element from an empty queue will 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.
| Constructor and Description |
|---|
ArrayBlockingDroppingQueue(int capacity)
Creates an ArrayBlockingDroppingQueue with the given (fixed)
capacity and default access policy.
|
ArrayBlockingDroppingQueue(int capacity,
boolean fair)
Creates an ArrayBlockingDroppingQueue with the given (fixed)
capacity and the specified access policy.
|
ArrayBlockingDroppingQueue(int capacity,
boolean fair,
Collection<? extends E> c)
Creates an ArrayBlockingDroppingQueue 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.
|
| Modifier and Type | Method and Description |
|---|---|
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.
|
void |
clear()
Atomically removes all of the elements from this queue.
|
boolean |
contains(Object o)
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.
|
long |
dropCount()
Returns the total number of items that have been dropped by this
BlockingDroppingQueue to make space for new elements within its
lifetime. |
long |
insertCount()
Returns the total number of items that have been inserted into this
BlockingDroppingQueue within its lifetime. |
Iterator<E> |
iterator()
Returns an iterator over the elements in this queue in proper sequence.
|
boolean |
offer(E e)
Inserts the specified element into this queue if it is possible to do so
immediately without violating capacity restrictions, returning
true upon success and false if no space is currently
available.
|
E |
peek() |
E |
poll() |
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.
|
E |
put(E e)
Inserts the specified element into this queue, dropping the oldest
element to make space if necessary.
|
int |
remainingCapacity()
Returns the number of additional elements that this queue can ideally (in
the absence of memory or resource constraints) accept without blocking.
|
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 queue.
|
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, in proper
sequence.
|
<T> 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.
|
String |
toString() |
addAll, element, removecontainsAll, isEmpty, removeAll, retainAllclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitaddAll, containsAll, equals, hashCode, isEmpty, parallelStream, removeAll, removeIf, retainAll, spliterator, streampublic ArrayBlockingDroppingQueue(int capacity)
capacity - the capacity of this queueIllegalArgumentException - if capacity is less than 1public ArrayBlockingDroppingQueue(int capacity, boolean fair)
capacity - the capacity of this queuefair - if true then queue accesses for threads blocked on
insertion or removal, are processed in FIFO order; if
false the access order is unspecified.IllegalArgumentException - if capacity is less than 1public ArrayBlockingDroppingQueue(int capacity, boolean fair, Collection<? extends E> c)
capacity - the capacity of this queuefair - 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 containIllegalArgumentException - if capacity is less than c.size(), or less
than 1.NullPointerException - if the specified collection or any of its elements are nullpublic E put(E e) throws InterruptedException
BlockingDroppingQueueput in interface BlockingDroppingQueue<E>e - the element to addInterruptedException - if interrupted while waitingpublic long insertCount()
BlockingDroppingQueueBlockingDroppingQueue within its lifetime.insertCount in interface BlockingDroppingQueue<E>public long dropCount()
BlockingDroppingQueueBlockingDroppingQueue to make space for new elements within its
lifetime.dropCount in interface BlockingDroppingQueue<E>public boolean add(E e)
add in interface Collection<E>add in interface Queue<E>add in interface BlockingDroppingQueue<E>add in class AbstractQueue<E>e - the element to addCollection.add(E))IllegalStateException - if this queue is fullNullPointerException - if the specified element is nullpublic boolean offer(E e)
BlockingDroppingQueueBlockingDroppingQueue.add(E), which can fail to insert an element
only by throwing an exception.public E take() throws InterruptedException
BlockingDroppingQueuetake in interface BlockingDroppingQueue<E>InterruptedException - if interrupted while waitingpublic E poll(long timeout, TimeUnit unit) throws InterruptedException
BlockingDroppingQueuepoll in interface BlockingDroppingQueue<E>timeout - how long to wait before giving up, in units of unitunit - a TimeUnit determining how to interpret the
timeout parameterInterruptedException - if interrupted while waitingpublic int size()
size in interface Collection<E>size in class AbstractCollection<E>public int remainingCapacity()
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 BlockingDroppingQueue<E>public boolean remove(Object o)
remove in interface Collection<E>remove in interface BlockingDroppingQueue<E>remove in class AbstractCollection<E>o - element to be removed from this queue, if presentpublic boolean contains(Object o)
contains in interface Collection<E>contains in interface BlockingDroppingQueue<E>contains in class AbstractCollection<E>o - object to be checked for containment in this queuepublic Object[] toArray()
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 class AbstractCollection<E>public <T> T[] toArray(T[] a)
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().
toArray in interface Collection<E>toArray in class 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 purposeArrayStoreException - if the runtime type of the specified array is not a supertype
of the runtime type of every element in this queueNullPointerException - if the specified array is nullpublic String toString()
toString in class AbstractCollection<E>public void clear()
clear in interface Collection<E>clear in class AbstractQueue<E>public int drainTo(Collection<? super E> c)
BlockingDroppingQueuedrainTo in interface BlockingDroppingQueue<E>c - the collection to transfer elements intoUnsupportedOperationException - if addition of elements is not supported by the specified
collectionClassCastException - if the class of an element of this queue prevents it from
being added to the specified collectionNullPointerException - if the specified collection is nullIllegalArgumentException - if the specified collection is this queue, or some property
of an element of this queue prevents it from being added to
the specified collectionpublic int drainTo(Collection<? super E> c, int maxElements)
BlockingDroppingQueuedrainTo in interface BlockingDroppingQueue<E>c - the collection to transfer elements intomaxElements - the maximum number of elements to transferUnsupportedOperationException - if addition of elements is not supported by the specified
collectionClassCastException - if the class of an element of this queue prevents it from
being added to the specified collectionNullPointerException - if the specified collection is nullIllegalArgumentException - if the specified collection is this queue, or some property
of an element of this queue prevents it from being added to
the specified collectionpublic Iterator<E> iterator()
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 Iterable<E>iterator in interface Collection<E>iterator in class AbstractCollection<E>