Package java.util.concurrent

Class ArrayBlockingQueue<E>

  • Type Parameters:
    E - the type of elements held in this queue
    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 changed. 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.

    Since:
    1.5
    See Also:
    Serialized Form

    • Constructor Summary

      Constructors 
      Constructor Description
      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

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method 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.
      Iterator<E> iterator()
      Returns an iterator over the elements in this queue in proper sequence.
      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.
      boolean offer​(E e, long timeout, TimeUnit unit)
      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.
      E peek()
      Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
      E poll()
      Retrieves and removes the head of this queue, or returns null if this queue is empty.
      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.
      void put​(E e)
      Inserts the specified element at the tail of this queue, waiting for space to become available if the queue is full.
      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()
      Returns the string representation of this Collection.

    • Constructor Detail

      • 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 < 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 < 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 the specified collection or any of its elements are null

    • Method Detail

      • 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.
        Specified by:
        add in interface BlockingQueue<E>
        Specified by:
        add in interface Collection<E>
        Specified by:
        add in interface Queue<E>
        Overrides:
        add in class AbstractQueue<E>
        Parameters:
        e - the element to add
        Returns:
        true (as specified by Collection.add(E))
        Throws:
        IllegalStateException - if this queue is full
        NullPointerException - if the specified element is null

      • 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.
        Specified by:
        offer in interface BlockingQueue<E>
        Specified by:
        offer in interface Queue<E>
        Parameters:
        e - the element to add
        Returns:
        true if the element was added to this queue, else false
        Throws:
        NullPointerException - if the specified element is null

      • 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.
        Specified by:
        offer in interface BlockingQueue<E>
        Parameters:
        e - 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 returns 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 up to the specified wait time if necessary for an element to become available.
        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 available
        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, or returns 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()
        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 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.

        Specified by:
        remainingCapacity in interface BlockingQueue<E>
        Returns:
        the remaining capacity

      • 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).

        Removal of interior elements in circular array based queues is an intrinsically slow and disruptive operation, so should be undertaken only in exceptional circumstances, ideally only when the queue is known not to be accessible by other threads.

        Specified by:
        remove in interface BlockingQueue<E>
        Specified by:
        remove in interface Collection<E>
        Overrides:
        remove in class AbstractCollection<E>
        Parameters:
        o - element to be removed from this queue, if present
        Returns:
        true if this queue changed as a result of the call

      • contains

        public boolean contains​(Object o)
        Returns true if this queue contains the specified element. More formally, returns true if and only if this queue contains at least one element e such that o.equals(e).
        Specified by:
        contains in interface BlockingQueue<E>
        Specified by:
        contains in interface Collection<E>
        Overrides:
        contains in class AbstractCollection<E>
        Parameters:
        o - object to be checked for containment in this queue
        Returns:
        true if this queue contains the specified element

      • 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.

        Specified by:
        toArray in interface Collection<E>
        Overrides:
        toArray in class AbstractCollection<E>
        Returns:
        an array containing all of the elements in this queue

      • toArray

        public <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. 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().
        Specified by:
        toArray in interface Collection<E>
        Overrides:
        toArray in class AbstractCollection<E>
        Parameters:
        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
        Returns:
        an array containing all of the elements in this queue
        Throws:
        ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue
        NullPointerException - if the specified array is null

      • toString

        public String toString()
        Description copied from class: AbstractCollection
        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).
        Overrides:
        toString in class AbstractCollection<E>
        Returns:
        the 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 to 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
        Throws:
        UnsupportedOperationException - if addition of elements is not supported by the specified collection
        ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection
        NullPointerException - if the specified collection is null
        IllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection

      • 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 to 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
        Throws:
        UnsupportedOperationException - if addition of elements is not supported by the specified collection
        ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection
        NullPointerException - if the specified collection is null
        IllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection

      • iterator

        public Iterator<E> iterator()
        Returns an iterator over the elements in this queue in proper sequence. The elements will be returned in order from first (head) to last (tail).

        The returned iterator is weakly consistent.

        Specified by:
        iterator in interface Collection<E>
        Specified by:
        iterator in interface Iterable<E>
        Specified by:
        iterator in class AbstractCollection<E>
        Returns:
        an iterator over the elements in this queue in proper sequence