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## java.util.concurrent
Class LinkedBlockingQueue<E>

    java.lang.Object
      java.util.AbstractCollection<E>
          java.util.AbstractQueue<E>
              java.util.concurrent.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

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

Method Summary
`void` | `clear()` Atomically removes all of the elements from this queue.
`int` | `drainTo(Collection<? super E> c)` Removes all available elements from this queue and adds them into 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 into the given collection.
`Iterator<E>` | `iterator()` Returns an iterator over the elements in this queue in proper sequence.
`boolean` | `offer(E o)` Inserts the specified element at the tail of this queue if possible, returning immediately if this queue is full.
`boolean` | `offer(E o, 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, returning `null` if this queue is empty.
`E` | `poll()` Retrieves and removes the head of this queue, or `null` if this queue is empty.
`E` | `poll(long timeout, TimeUnit unit)` Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements are present on this queue.
`void` | `put(E o)` Adds the specified element to the tail of this queue, waiting if necessary for space to become available.
`int` | `remainingCapacity()` Returns the number of 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 no elements are present on this queue.
`Object[]` | `toArray()` Returns an array containing all of the elements in this collection.
`
`<T> T[]`
` | `toArray(T[] a)` Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
`String` | `toString()` Returns a string representation of this collection.

Methods inherited from class java.util.AbstractQueue
`add, addAll, element, remove`

Methods inherited from class java.util.AbstractCollection
`contains, containsAll, isEmpty, removeAll, retainAll`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Methods inherited from interface java.util.concurrent.BlockingQueue
`add`

Methods inherited from interface java.util.Queue
`element, remove`

Methods inherited from interface java.util.Collection
`addAll, contains, containsAll, equals, hashCode, isEmpty, removeAll, retainAll`

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 `c` or any element within it is `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 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 `add` an element will succeed by inspecting `remainingCapacity` because it may be the case that a waiting consumer is ready to `take` an element out of an otherwise full queue.

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

### put

    public void put(E o)
             throws InterruptedException

  Adds the specified element to the tail of this queue, waiting if necessary for space to become available.

  Specified by:
    `put` in interface `BlockingQueue<E>`
  Parameters:
    `o` - the element to add
  Throws:
    `InterruptedException` - if interrupted while waiting.
    `NullPointerException` - if the specified element is `null`.

### offer

    public boolean offer(E o,
                         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:
    `o` - 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 o)

  Inserts the specified element at the tail of this queue if possible, returning immediately if this queue is full.

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

### take

    public E take()
           throws InterruptedException

  Description copied from interface: `BlockingQueue`
  Retrieves and removes the head of this queue, waiting if no elements are present on this queue.

  Specified by:
    `take` in interface `BlockingQueue<E>`
  Returns:
    the head of this queue
  Throws:
    `InterruptedException` - if interrupted while waiting.

### poll

    public E poll(long timeout,
                  TimeUnit unit)
           throws InterruptedException

  Description copied from interface: `BlockingQueue`
  Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements are present on this queue.

  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 present.
  Throws:
    `InterruptedException` - if interrupted while waiting.

### poll

    public E poll()

  Description copied from interface: `Queue`
  Retrieves and removes the head of this queue, or `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, returning `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.

  Specified by:
    `remove` in interface `Collection<E>`
  Overrides:
    `remove` in class `AbstractCollection<E>`
  Parameters:
    `o` - element to be removed from this collection, if present.
  Returns:
    `true` if the collection contained the specified element.

### toArray

    public Object[] toArray()

  Description copied from class: `AbstractCollection`
  Returns an array containing all of the elements in this collection. If the collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array will be "safe" in that no references to it are maintained by the collection. (In other words, this method must allocate a new array even if the collection is backed by an Array). The caller is thus free to modify the returned array.

  This implementation allocates the array to be returned, and iterates over the elements in the collection, storing each object reference in the next consecutive element of the array, starting with element 0.

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

### toArray

    public <T> T[] toArray(T[] a)

  Description copied from class: `AbstractCollection`
  Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection 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 collection.

  If the collection fits in the specified array with room to spare (i.e., the array has more elements than the collection), the element in the array immediately following the end of the collection is set to `null`. This is useful in determining the length of the collection only if the caller knows that the collection does not contain any `null` elements.)

  If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

  This implementation checks if the array is large enough to contain the collection; if not, it allocates a new array of the correct size and type (using reflection). Then, it iterates over the collection, storing each object reference in the next consecutive element of the array, starting with element 0. If the array is larger than the collection, a `null` is stored in the first location after the end of the collection.

  Specified by:
    `toArray` in interface `Collection<E>`
  Overrides:
    `toArray` in class `AbstractCollection<E>`
  Parameters:
    `a` - the array into which the elements of the collection 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 the elements of the collection.

### 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)`.

  This implementation creates an empty string buffer, appends a left square bracket, and iterates over the collection appending the string representation of each element in turn. After appending each element except the last, the string `", "` is appended. Finally a right bracket is appended. A string is obtained from the string buffer, and returned.

  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 into 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.

### 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 into 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.

### iterator

    public Iterator<E> 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 `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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