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Java compact1, compact2, compact3 java.util.concurrent Class LinkedBlockingQueue<E>（JDK8）

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Java™ Platform
Standard Ed. 8
compact1, compact2, compact3
java.util.concurrent

Class LinkedBlockingQueue<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 LinkedBlockingQueue<E>
extends AbstractQueue<E>
implements BlockingQueue<E>, Serializable
    An optionally-bounded blocking queue based on linked nodes. 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. Linked queues typically have higher throughput than array-based queues but less predictable performance in most concurrent applications.

    The optional capacity bound constructor argument serves as a way to prevent excessive queue expansion. The capacity, if unspecified, is equal to Integer.MAX_VALUE. Linked nodes are dynamically created upon each insertion unless this would bring the queue above capacity.

    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

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method and Description
      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 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, 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 if necessary for space to become available.
      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.
      Spliterator<E> spliterator()
      Returns a Spliterator over the 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 a string representation of this collection.

    • Constructor Detail

      • LinkedBlockingQueue

        public LinkedBlockingQueue()
        Creates a LinkedBlockingQueue with a capacity of Integer.MAX_VALUE.

      • LinkedBlockingQueue

        public LinkedBlockingQueue(int capacity)
        Creates a LinkedBlockingQueue with the given (fixed) capacity.
        Parameters:
        capacity - the capacity of this queue
        Throws:
        IllegalArgumentException - if capacity is not greater than zero

      • LinkedBlockingQueue

        public LinkedBlockingQueue(Collection<? extends E> c)
        Creates a LinkedBlockingQueue with a capacity of Integer.MAX_VALUE, initially containing the elements of the given collection, added in traversal order of the collection's iterator.
        Parameters:
        c - the collection of elements to initially contain
        Throws:
        NullPointerException - if the specified collection or any of its elements are null

    • Method Detail

      • 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

      • offer

        public boolean offer(E e,
                     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:
        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

      • 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. When using a capacity-restricted queue, this method is generally preferable to method add, 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

      • 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

      • 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

      • 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

      • 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).
        Specified by:
        remove in interface Collection<E>
        Specified by:
        remove in interface BlockingQueue<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 Collection<E>
        Specified by:
        contains in interface BlockingQueue<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>
        Type Parameters:
        T - the runtime type of the array to contain the collection
        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 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).
        Overrides:
        toString in class AbstractCollection<E>
        Returns:
        a string representation of this collection

      • clear

        public void clear()
        Atomically removes all of the elements from this queue. The queue will be empty after this call returns.
        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 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 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
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Java™ Platform
Standard Ed. 8

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For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2022, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.

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