java.util.concurrent

Class LinkedBlockingQueue<E>

Implemented Interfaces:
BlockingQueue<E>, Collection<E>, Iterable<E>, Queue<E>, Serializable

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 ../../../../technotes/guides/collections/index.html"> Java Collections Framework.

Since:
1.5
See Also:
Serialized Form

Constructor Summary

LinkedBlockingQueue()
Creates a LinkedBlockingQueue with a capacity of Integer.MAX_VALUE.
LinkedBlockingQueue(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.
LinkedBlockingQueue(int capacity)
Creates a LinkedBlockingQueue with the given (fixed) capacity.

Method Summary

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.
void
clear()
Atomically removes all of the elements from this queue.
int
drainTo(E> c)
int
drainTo(E> c, int maxElements)
Iterator
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)
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.
E
take()
Object[]
toArray()
Returns an array containing all of the elements in this queue, in proper sequence.
String
toString()

Methods inherited from class java.util.AbstractQueue<E>

add, addAll, clear, element, remove

Methods inherited from class java.util.AbstractCollection<E>

T[] toArray, add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toString

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

LinkedBlockingQueue

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

LinkedBlockingQueue

public LinkedBlockingQueue(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

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

Method Details

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().
Specified by:
T[] toArray in interface Collection<E>
Overrides:
T[] toArray in interface 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

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 interface AbstractQueue<E>

drainTo

public int drainTo(E> c)
Specified by:
drainTo in interface BlockingQueue<E>

drainTo

public int drainTo(E> c,
                   int maxElements)
Specified by:
drainTo in interface BlockingQueue<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.
Specified by:
iterator in interface Collection<E>
iterator in interface Iterable<E>
Overrides:
iterator in interface AbstractCollection<E>
Returns:
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. 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>
offer in interface Queue<E>
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 if necessary up to the specified wait time for space to become available.
Specified by:
offer in interface BlockingQueue<E>
Returns:
true if successful, or false if the specified waiting time elapses before space is available.

peek

public E peek()
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

poll

public E poll()
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
Specified by:
poll in interface BlockingQueue<E>

put

public void put(E e)
            throws InterruptedException
Inserts the specified element at the tail of this queue, waiting if necessary for space to become available.
Specified by:
put 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.

Specified by:
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).
Specified by:
remove in interface BlockingQueue<E>
remove in interface Collection<E>
Overrides:
remove in interface 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

size

public int size()
Returns the number of elements in this queue.
Specified by:
size in interface Collection<E>
Overrides:
size in interface AbstractCollection<E>
Returns:
the number of elements in this queue

take

public E take()
            throws InterruptedException
Specified by:
take in interface BlockingQueue<E>

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 interface AbstractCollection<E>
Returns:
an array containing all of the elements in this queue

toString

public String toString()
Overrides:
toString in interface AbstractCollection<E>