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LinkedBlockingDeque

public class LinkedBlockingDeque
extends AbstractQueue<E> implements BlockingDeque<E>, Serializable

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


An optionally-bounded blocking deque based on linked nodes.

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

Most operations run in constant time (ignoring time spent blocking). Exceptions include remove, removeFirstOccurrence, removeLastOccurrence, contains, iterator.remove(), and the bulk operations, all of which run in linear time.

This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces.

Summary

Public constructors

LinkedBlockingDeque()

Creates a LinkedBlockingDeque with a capacity of MAX_VALUE.

LinkedBlockingDeque(int capacity)

Creates a LinkedBlockingDeque with the given (fixed) capacity.

LinkedBlockingDeque(Collection<? extends E> c)

Creates a LinkedBlockingDeque with a capacity of MAX_VALUE, initially containing the elements of the given collection, added in traversal order of the collection's iterator.

Public methods

boolean add(E e)

Inserts the specified element at the end of this deque unless it would violate capacity restrictions.

void addFirst(E e)

Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.

void addLast(E e)

Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.

void clear()

Atomically removes all of the elements from this deque.

boolean contains(Object o)

Returns true if this deque contains the specified element.

Iterator<E> descendingIterator()

Returns an iterator over the elements in this deque in reverse sequential order.

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.

E element()

Retrieves, but does not remove, the head of the queue represented by this deque.

E getFirst()

Retrieves, but does not remove, the first element of this deque.

E getLast()

Retrieves, but does not remove, the last element of this deque.

Iterator<E> iterator()

Returns an iterator over the elements in this deque in proper sequence.

boolean offer(E e, long timeout, TimeUnit unit)

Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting up to the specified wait time if necessary for space to become available.

boolean offer(E e)

Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available.

boolean offerFirst(E e)

Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available.

boolean offerFirst(E e, long timeout, TimeUnit unit)

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

boolean offerLast(E e)

Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available.

boolean offerLast(E e, long timeout, TimeUnit unit)

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

E peek()

Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.

E peekFirst()

Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.

E peekLast()

Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.

E poll(long timeout, TimeUnit unit)

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting up to the specified wait time if necessary for an element to become available.

E poll()

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.

E pollFirst()

Retrieves and removes the first element of this deque, or returns null if this deque is empty.

E pollFirst(long timeout, TimeUnit unit)

Retrieves and removes the first element of this deque, waiting up to the specified wait time if necessary for an element to become available.

E pollLast(long timeout, TimeUnit unit)

Retrieves and removes the last element of this deque, waiting up to the specified wait time if necessary for an element to become available.

E pollLast()

Retrieves and removes the last element of this deque, or returns null if this deque is empty.

E pop()

Pops an element from the stack represented by this deque.

void push(E e)

Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.

void put(E e)

Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting if necessary for space to become available.

void putFirst(E e)

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

void putLast(E e)

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

int remainingCapacity()

Returns the number of additional elements that this deque can ideally (in the absence of memory or resource constraints) accept without blocking.

E remove()

Retrieves and removes the head of the queue represented by this deque.

boolean remove(Object o)

Removes the first occurrence of the specified element from this deque.

E removeFirst()

Retrieves and removes the first element of this deque.

boolean removeFirstOccurrence(Object o)

Removes the first occurrence of the specified element from this deque.

E removeLast()

Retrieves and removes the last element of this deque.

boolean removeLastOccurrence(Object o)

Removes the last occurrence of the specified element from this deque.

int size()

Returns the number of elements in this deque.

Spliterator<E> spliterator()

Returns a Spliterator over the elements in this deque.

E take()

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting if necessary until an element becomes available.

E takeFirst()

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

E takeLast()

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

Object[] toArray()

Returns an array containing all of the elements in this deque, in proper sequence (from first to last element).

<T> T[] toArray(T[] a)

Returns an array containing all of the elements in this deque, 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.

Inherited methods

From class java.util.AbstractQueue
From class java.util.AbstractCollection
From class java.lang.Object
From interface java.util.Queue
From interface java.util.Collection
From interface java.util.concurrent.BlockingDeque
From interface java.lang.Iterable
From interface java.util.concurrent.BlockingQueue
From interface java.util.Deque

Public constructors

LinkedBlockingDeque

Added in API level 9
LinkedBlockingDeque ()

Creates a LinkedBlockingDeque with a capacity of MAX_VALUE.

LinkedBlockingDeque

Added in API level 9
LinkedBlockingDeque (int capacity)

Creates a LinkedBlockingDeque with the given (fixed) capacity.

Parameters
capacity int: the capacity of this deque
Throws
IllegalArgumentException if capacity is less than 1

LinkedBlockingDeque

Added in API level 9
LinkedBlockingDeque (Collection<? extends E> c)

Creates a LinkedBlockingDeque with a capacity of 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

add

Added in API level 9
boolean add (E e)

Inserts the specified element at the end of this deque unless it would violate capacity restrictions. When using a capacity-restricted deque, it is generally preferable to use method offer.

This method is equivalent to addLast(E).

Parameters
e E: the element to add
Returns
boolean true (as specified by add(E))
Throws
IllegalStateException if this deque is full
NullPointerException if the specified element is null

addFirst

Added in API level 9
void addFirst (E e)

Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use offerFirst.

Parameters
e E: the element to add
Throws
IllegalStateException if this deque is full
NullPointerException

addLast

Added in API level 9
void addLast (E e)

Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use offerLast.

Parameters
e E: the element to add
Throws
IllegalStateException if this deque is full
NullPointerException

clear

Added in API level 9
void clear ()

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

contains

Added in API level 9
boolean contains (Object o)

Returns true if this deque contains the specified element. More formally, returns true if and only if this deque contains at least one element e such that o.equals(e).

Parameters
o Object: object to be checked for containment in this deque
Returns
boolean true if this deque contains the specified element

descendingIterator

Added in API level 9
Iterator<E> descendingIterator ()

Returns an iterator over the elements in this deque in reverse sequential order. The elements will be returned in order from last (tail) to first (head).

The returned iterator is weakly consistent.

Returns
Iterator<E> an iterator over the elements in this deque in reverse order

drainTo

Added in API level 9
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

Added in API level 9
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

element

Added in API level 9
E element ()

Retrieves, but does not remove, the head of the queue represented by this deque. This method differs from peek only in that it throws an exception if this deque is empty.

This method is equivalent to getFirst.

Returns
E the head of the queue represented by this deque
Throws
NoSuchElementException if this deque is empty

getFirst

Added in API level 9
E getFirst ()

Retrieves, but does not remove, the first element of this deque. This method differs from peekFirst only in that it throws an exception if this deque is empty.

Returns
E the head of this deque
Throws
NoSuchElementException

getLast

Added in API level 9
E getLast ()

Retrieves, but does not remove, the last element of this deque. This method differs from peekLast only in that it throws an exception if this deque is empty.

Returns
E the tail of this deque
Throws
NoSuchElementException

iterator

Added in API level 9
Iterator<E> iterator ()

Returns an iterator over the elements in this deque 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 deque in proper sequence

offer

Added in API level 9
boolean offer (E e, 
                long timeout, 
                TimeUnit unit)

Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting up to the specified wait time if necessary for space to become available.

This method is equivalent to offerLast.

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 the element was added to this deque, else false
Throws
NullPointerException
InterruptedException

offer

Added in API level 9
boolean offer (E e)

Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to the add(E) method, which can fail to insert an element only by throwing an exception.

This method is equivalent to offerLast.

Parameters
e E: the element to add
Returns
boolean true if the element was added to this deque, else false
Throws
NullPointerException if the specified element is null

offerFirst

Added in API level 9
boolean offerFirst (E e)

Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to the addFirst method, 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 deque, else false
Throws
NullPointerException

offerFirst

Added in API level 9
boolean offerFirst (E e, 
                long timeout, 
                TimeUnit unit)

Inserts the specified element at the front of this deque, waiting up to the specified wait time if necessary 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
NullPointerException
InterruptedException

offerLast

Added in API level 9
boolean offerLast (E e)

Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to the addLast method, 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 deque, else false
Throws
NullPointerException

offerLast

Added in API level 9
boolean offerLast (E e, 
                long timeout, 
                TimeUnit unit)

Inserts the specified element at the end of this deque, waiting up to the specified wait time if necessary 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
NullPointerException
InterruptedException

peek

Added in API level 9
E peek ()

Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.

This method is equivalent to peekFirst.

Returns
E the head of this deque, or null if this deque is empty

peekFirst

Added in API level 9
E peekFirst ()

Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.

Returns
E the head of this deque, or null if this deque is empty

peekLast

Added in API level 9
E peekLast ()

Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.

Returns
E the tail of this deque, or null if this deque is empty

poll

Added in API level 9
E poll (long timeout, 
                TimeUnit unit)

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting up to the specified wait time if necessary for an element to become available.

This method is equivalent to pollFirst.

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 deque, or null if the specified waiting time elapses before an element is available
Throws
InterruptedException

poll

Added in API level 9
E poll ()

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.

This method is equivalent to pollFirst().

Returns
E the head of this deque, or null if this deque is empty

pollFirst

Added in API level 9
E pollFirst ()

Retrieves and removes the first element of this deque, or returns null if this deque is empty.

Returns
E the head of this deque, or null if this deque is empty

pollFirst

Added in API level 9
E pollFirst (long timeout, 
                TimeUnit unit)

Retrieves and removes the first element of this deque, 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 deque, or null if the specified waiting time elapses before an element is available
Throws
InterruptedException

pollLast

Added in API level 9
E pollLast (long timeout, 
                TimeUnit unit)

Retrieves and removes the last element of this deque, 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 tail of this deque, or null if the specified waiting time elapses before an element is available
Throws
InterruptedException

pollLast

Added in API level 9
E pollLast ()

Retrieves and removes the last element of this deque, or returns null if this deque is empty.

Returns
E the tail of this deque, or null if this deque is empty

pop

Added in API level 9
E pop ()

Pops an element from the stack represented by this deque. In other words, removes and returns the first element of this deque.

This method is equivalent to removeFirst().

Returns
E the element at the front of this deque (which is the top of the stack represented by this deque)
Throws
NoSuchElementException

push

Added in API level 9
void push (E e)

Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.

This method is equivalent to addFirst.

Parameters
e E: the element to push
Throws
IllegalStateException if this deque is full
NullPointerException

put

Added in API level 9
void put (E e)

Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting if necessary for space to become available.

This method is equivalent to putLast.

Parameters
e E: the element to add
Throws
NullPointerException
InterruptedException

putFirst

Added in API level 9
void putFirst (E e)

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

Parameters
e E: the element to add
Throws
NullPointerException
InterruptedException

putLast

Added in API level 9
void putLast (E e)

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

Parameters
e E: the element to add
Throws
NullPointerException
InterruptedException

remainingCapacity

Added in API level 9
int remainingCapacity ()

Returns the number of additional elements that this deque can ideally (in the absence of memory or resource constraints) accept without blocking. This is always equal to the initial capacity of this deque less the current size of this deque.

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

Added in API level 9
E remove ()

Retrieves and removes the head of the queue represented by this deque. This method differs from poll only in that it throws an exception if this deque is empty.

This method is equivalent to removeFirst.

Returns
E the head of the queue represented by this deque
Throws
NoSuchElementException if this deque is empty

remove

Added in API level 9
boolean remove (Object o)

Removes the first occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first element e such that o.equals(e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

This method is equivalent to removeFirstOccurrence.

Parameters
o Object: element to be removed from this deque, if present
Returns
boolean true if this deque changed as a result of the call

removeFirst

Added in API level 9
E removeFirst ()

Retrieves and removes the first element of this deque. This method differs from pollFirst only in that it throws an exception if this deque is empty.

Returns
E the head of this deque
Throws
NoSuchElementException

removeFirstOccurrence

Added in API level 9
boolean removeFirstOccurrence (Object o)

Removes the first occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first element e such that o.equals(e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

Parameters
o Object: element to be removed from this deque, if present
Returns
boolean true if an element was removed as a result of this call

removeLast

Added in API level 9
E removeLast ()

Retrieves and removes the last element of this deque. This method differs from pollLast only in that it throws an exception if this deque is empty.

Returns
E the tail of this deque
Throws
NoSuchElementException

removeLastOccurrence

Added in API level 9
boolean removeLastOccurrence (Object o)

Removes the last occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the last element e such that o.equals(e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

Parameters
o Object: element to be removed from this deque, if present
Returns
boolean true if an element was removed as a result of this call

size

Added in API level 9
int size ()

Returns the number of elements in this deque.

Returns
int the number of elements in this deque

spliterator

Added in API level 24
Spliterator<E> spliterator ()

Returns a Spliterator over the elements in this deque.

The returned spliterator is weakly consistent.

The Spliterator reports CONCURRENT, ORDERED, and NONNULL.

Implementation Note:
  • The Spliterator implements trySplit to permit limited parallelism.
Returns
Spliterator<E> a Spliterator over the elements in this deque

take

Added in API level 9
E take ()

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting if necessary until an element becomes available.

This method is equivalent to takeFirst.

Returns
E the head of this deque
Throws
InterruptedException

takeFirst

Added in API level 9
E takeFirst ()

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

Returns
E the head of this deque
Throws
InterruptedException

takeLast

Added in API level 9
E takeLast ()

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

Returns
E the tail of this deque
Throws
InterruptedException

toArray

Added in API level 9
Object[] toArray ()

Returns an array containing all of the elements in this deque, in proper sequence (from first to last element).

The returned array will be "safe" in that no references to it are maintained by this deque. (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 deque

toArray

Added in API level 9
T[] toArray (T[] a)

Returns an array containing all of the elements in this deque, in proper sequence; the runtime type of the returned array is that of the specified array. If the deque 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 deque.

If this deque fits in the specified array with room to spare (i.e., the array has more elements than this deque), the element in the array immediately following the end of the deque 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 deque known to contain only strings. The following code can be used to dump the deque 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 deque 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 deque
Throws
ArrayStoreException if the runtime type of the specified array is not a supertype of the runtime type of every element in this deque
NullPointerException if the specified array is null

toString

Added in API level 9
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 valueOf(Object).

Returns
String a string representation of this collection
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