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Summary: Ctors | Methods | Inherited Methods

# LinkedBlockingQueue

`public class LinkedBlockingQueue`
`` `` `extends AbstractQueue<E>` `implements BlockingQueue<E>, Serializable`

java.lang.Object
↳ | java.util.AbstractCollection<E>
| ↳ | java.util.AbstractQueue<E>
|  | ↳ | java.util.concurrent.LinkedBlockingQueue<E>

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.

## Summary

### Public constructors
`LinkedBlockingQueue()` Creates a `LinkedBlockingQueue` with a capacity of `Integer#MAX_VALUE`.
`LinkedBlockingQueue(int capacity)` Creates a `LinkedBlockingQueue` with the given (fixed) capacity.
`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.

### Public methods
`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, int maxElements)` Removes at most the given number of available elements from this queue and adds them to the given collection.
`int` | `drainTo(Collection<? super E> c)` Removes all 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(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` | `poll()` Retrieves and removes the head of this queue, or returns `null` if this queue is empty.
`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.
`<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.
`Object[]` | `toArray()` Returns an array containing all of the elements in this queue, in proper sequence.
`String` | `toString()` Returns a string representation of this collection.

### Inherited methods
From class `java.util.AbstractQueue`
`boolean` | `add(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 throwing an `IllegalStateException` if no space is currently available.
`boolean` | `addAll(Collection<? extends E> c)` Adds all of the elements in the specified collection to this queue.
`void` | `clear()` Removes all of the elements from this queue.
`E` | `element()` Retrieves, but does not remove, the head of this queue.
`E` | `remove()` Retrieves and removes the head of this queue.
From class `java.util.AbstractCollection`
`boolean` | `add(E e)` Ensures that this collection contains the specified element (optional operation). This implementation always throws an `UnsupportedOperationException`.
`boolean` | `addAll(Collection<? extends E> c)` Adds all of the elements in the specified collection to this collection (optional operation). This implementation iterates over the specified collection, and adds each object returned by the iterator to this collection, in turn.
`void` | `clear()` Removes all of the elements from this collection (optional operation). This implementation iterates over this collection, removing each element using the `Iterator.remove` operation.
`boolean` | `contains(Object o)` Returns `true` if this collection contains the specified element. This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.
`boolean` | `containsAll(Collection<?> c)` Returns `true` if this collection contains all of the elements in the specified collection. This implementation iterates over the specified collection, checking each element returned by the iterator in turn to see if it's contained in this collection.
`boolean` | `isEmpty()` Returns `true` if this collection contains no elements. This implementation returns `size() == 0`.
`abstract Iterator<E>` | `iterator()` Returns an iterator over the elements contained in this collection.
`boolean` | `remove(Object o)` Removes a single instance of the specified element from this collection, if it is present (optional operation). This implementation iterates over the collection looking for the specified element.
`boolean` | `removeAll(Collection<?> c)` Removes all of this collection's elements that are also contained in the specified collection (optional operation). This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection.
`boolean` | `retainAll(Collection<?> c)` Retains only the elements in this collection that are contained in the specified collection (optional operation). This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection.
`abstract int` | `size()` Returns the number of 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. This implementation returns an array containing all the elements returned by this collection's iterator in the same order, stored in consecutive elements of the array, starting with index `0`.
`Object[]` | `toArray()` Returns an array containing all of the elements in this collection. This implementation returns an array containing all the elements returned by this collection's iterator, in the same order, stored in consecutive elements of the array, starting with index `0`.
`String` | `toString()` Returns a string representation of this collection.
From class `java.lang.Object`
`Object` | `clone()` Creates and returns a copy of this object.
`boolean` | `equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void` | `finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>` | `getClass()` Returns the runtime class of this `Object`.
`int` | `hashCode()` Returns a hash code value for the object.
`final void` | `notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void` | `notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String` | `toString()` Returns a string representation of the object.
`final void` | `wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void` | `wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.
From interface `java.util.Queue`
`abstract boolean` | `add(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 throwing an `IllegalStateException` if no space is currently available.
`abstract E` | `element()` Retrieves, but does not remove, the head of this queue.
`abstract boolean` | `offer(E e)` Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions.
`abstract E` | `peek()` Retrieves, but does not remove, the head of this queue, or returns `null` if this queue is empty.
`abstract E` | `poll()` Retrieves and removes the head of this queue, or returns `null` if this queue is empty.
`abstract E` | `remove()` Retrieves and removes the head of this queue.
From interface `java.util.Collection`
`abstract boolean` | `add(E e)` Ensures that this collection contains the specified element (optional operation).
`abstract boolean` | `addAll(Collection<? extends E> c)` Adds all of the elements in the specified collection to this collection (optional operation).
`abstract void` | `clear()` Removes all of the elements from this collection (optional operation).
`abstract boolean` | `contains(Object o)` Returns `true` if this collection contains the specified element.
`abstract boolean` | `containsAll(Collection<?> c)` Returns `true` if this collection contains all of the elements in the specified collection.
`abstract boolean` | `equals(Object o)` Compares the specified object with this collection for equality.
`abstract int` | `hashCode()` Returns the hash code value for this collection.
`abstract boolean` | `isEmpty()` Returns `true` if this collection contains no elements.
`abstract Iterator<E>` | `iterator()` Returns an iterator over the elements in this collection.
`default Stream<E>` | `parallelStream()` Returns a possibly parallel `Stream` with this collection as its source.
`abstract boolean` | `remove(Object o)` Removes a single instance of the specified element from this collection, if it is present (optional operation).
`abstract boolean` | `removeAll(Collection<?> c)` Removes all of this collection's elements that are also contained in the specified collection (optional operation).
`default boolean` | `removeIf(Predicate<? super E> filter)` Removes all of the elements of this collection that satisfy the given predicate.
`abstract boolean` | `retainAll(Collection<?> c)` Retains only the elements in this collection that are contained in the specified collection (optional operation).
`abstract int` | `size()` Returns the number of elements in this collection.
`default Spliterator<E>` | `spliterator()` Creates a `Spliterator` over the elements in this collection.
`default Stream<E>` | `stream()` Returns a sequential `Stream` with this collection as its source.
`abstract <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.
`abstract Object[]` | `toArray()` Returns an array containing all of the elements in this collection.
From interface `java.util.concurrent.BlockingQueue`
`abstract boolean` | `add(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 throwing an `IllegalStateException` if no space is currently available.
`abstract boolean` | `contains(Object o)` Returns `true` if this queue contains the specified element.
`abstract int` | `drainTo(Collection<? super E> c)` Removes all available elements from this queue and adds them to the given collection.
`abstract 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.
`abstract 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.
`abstract boolean` | `offer(E e, long timeout, TimeUnit unit)` Inserts the specified element into this queue, waiting up to the specified wait time if necessary for space to become available.
`abstract 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.
`abstract void` | `put(E e)` Inserts the specified element into this queue, waiting if necessary for space to become available.
`abstract int` | `remainingCapacity()` Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking, or `Integer.MAX_VALUE` if there is no intrinsic limit.
`abstract boolean` | `remove(Object o)` Removes a single instance of the specified element from this queue, if it is present.
`abstract E` | `take()` Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
From interface `java.lang.Iterable`
`default void` | `forEach(Consumer<? super T> action)` Performs the given action for each element of the `Iterable` until all elements have been processed or the action throws an exception.
`abstract Iterator<E>` | `iterator()` Returns an iterator over elements of type `T`.
`default Spliterator<E>` | `spliterator()` Creates a `Spliterator` over the elements described by this `Iterable`.

## Public constructors

### 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` | `int`: 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` | `Collection`: the collection of elements to initially contain

Throws
`NullPointerException` | if the specified collection or any of its elements are null

## Public methods

### clear

    public void clear ()

Atomically removes all of the elements from this queue. The queue will be empty after this call returns.

### 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)`.

Parameters
`o` | `Object`: object to be checked for containment in this queue

Returns
`boolean` | `true` if this queue contains the specified element

### drainTo

    public 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. 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.

Parameters
`c` | `Collection`: the collection to transfer elements into
`maxElements` | `int`: the maximum number of elements to transfer

Returns
`int` | the number of elements transferred

Throws
`UnsupportedOperationException` |
`ClassCastException` |
`NullPointerException` |
`IllegalArgumentException` |

### drainTo

    public int drainTo (Collection<? super E> c)

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.

Parameters
`c` | `Collection`: the collection to transfer elements into

Returns
`int` | the number of elements transferred

Throws
`UnsupportedOperationException` |
`ClassCastException` |
`NullPointerException` |
`IllegalArgumentException` |

### 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.

Returns
`Iterator<E>` | 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.

Parameters
`e` | `E`: the element to add

Returns
`boolean` | `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)

Inserts the specified element at the tail of this queue, waiting if necessary up to the specified wait time for space to become available.

Parameters
`e` | `E`: the element to add
`timeout` | `long`: how long to wait before giving up, in units of `unit`
`unit` | `TimeUnit`: a `TimeUnit` determining how to interpret the `timeout` parameter

Returns
`boolean` | `true` if successful, or `false` if the specified waiting time elapses before space is available

Throws
`InterruptedException` |
`NullPointerException` |

### peek

    public E peek ()

Retrieves, but does not remove, the head of this queue, or returns `null` if this queue is empty.

Returns
`E` | the head of this queue, or `null` if this queue is empty

### poll

    public 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.

Parameters
`timeout` | `long`: how long to wait before giving up, in units of `unit`
`unit` | `TimeUnit`: a `TimeUnit` determining how to interpret the `timeout` parameter

Returns
`E` | the head of this queue, or `null` if the specified waiting time elapses before an element is available

Throws
`InterruptedException` |

### poll

    public E poll ()

Retrieves and removes the head of this queue, or returns `null` if this queue is empty.

Returns
`E` | the head of this queue, or `null` if this queue is empty

### put

    public void put (E e)

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

Parameters
`e` | `E`: the element to add

Throws
`InterruptedException` |
`NullPointerException` |

### 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.

Returns
`int` | 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).

Parameters
`o` | `Object`: element to be removed from this queue, if present

Returns
`boolean` | `true` if this queue changed as a result of the call

### size

    public int size ()

Returns the number of elements in this queue.

Returns
`int` | the number of elements in this queue

### spliterator

    public Spliterator<E> spliterator ()

Returns a `Spliterator` over the elements in this queue.

The returned spliterator is weakly consistent.

The `Spliterator` reports `Spliterator#CONCURRENT`, `Spliterator#ORDERED`, and `Spliterator#NONNULL`.

##### Implementation Note:

- The `Spliterator` implements `trySplit` to permit limited parallelism.

Returns
`Spliterator<E>` | a `Spliterator` over the elements in this queue

### take

    public E take ()

Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.

Returns
`E` | the head of this queue

Throws
`InterruptedException` |

### 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()`.

Parameters
`a` | `T`: 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
`T[]` | 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

### 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.

Returns
`Object[]` | an array containing all of the elements in this queue

### toString

    public String toString ()

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)`.

Returns
`String` | a string representation of this collection

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