LinkedBlockingDeque

AI-generated Key Takeaways

• LinkedBlockingDeque is a thread-safe, double-ended queue implemented using a linked list, offering optional capacity restrictions.

• It provides efficient insertion and retrieval operations, with most methods having constant-time complexity.

• LinkedBlockingDeque supports blocking operations, making it suitable for managing data flow between threads in concurrent environments.

• It offers a wide range of methods for element manipulation, catering to both deque and stack-like operations.

• The deque can be optionally bounded, providing flexibility in capacity management.

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

An optionally-bounded {@linkplain BlockingDeque 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 Integer.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.

Public Constructor Summary

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

Public Method Summary

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 Method Summary

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[] contents) 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) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of 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.
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).
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.
Spliterator<E>	spliterator() Creates a Spliterator over the elements in this collection.
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.BlockingDeque

abstract boolean	add(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 throwing an IllegalStateException if no space is currently available.
abstract 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.
abstract 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.
abstract boolean	contains(Object o) Returns true if this deque contains the specified element.
abstract E	element() Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque).
abstract Iterator<E>	iterator() Returns an iterator over the elements in this deque in proper sequence.
abstract 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.
abstract 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.
abstract 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.
abstract 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.
abstract 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.
abstract 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.
abstract 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.
abstract 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.
abstract 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.
abstract 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.
abstract 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.
abstract 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.
abstract 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.
abstract void	putFirst(E e) Inserts the specified element at the front of this deque, waiting if necessary for space to become available.
abstract void	putLast(E e) Inserts the specified element at the end of this deque, waiting if necessary for space to become available.
abstract E	remove() Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).
abstract boolean	remove(Object o) Removes the first occurrence of the specified element from this deque.
abstract boolean	removeFirstOccurrence(Object o) Removes the first occurrence of the specified element from this deque.
abstract boolean	removeLastOccurrence(Object o) Removes the last occurrence of the specified element from this deque.
abstract int	size() Returns the number of elements in this deque.
abstract 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.
abstract E	takeFirst() Retrieves and removes the first element of this deque, waiting if necessary until an element becomes available.
abstract E	takeLast() Retrieves and removes the last element of this deque, waiting if necessary until an element becomes available.

From interface java.lang.Iterable

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.
Spliterator<E>	spliterator() Creates a Spliterator over the elements described by this Iterable.

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.util.Deque

abstract boolean	add(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 throwing an IllegalStateException if no space is currently available.
abstract 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.
abstract 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.
abstract boolean	contains(Object o) Returns true if this deque contains the specified element.
abstract Iterator<E>	descendingIterator() Returns an iterator over the elements in this deque in reverse sequential order.
abstract E	element() Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque).
abstract E	getFirst() Retrieves, but does not remove, the first element of this deque.
abstract E	getLast() Retrieves, but does not remove, the last element of this deque.
abstract Iterator<E>	iterator() Returns an iterator over the elements in this deque in proper sequence.
abstract 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.
abstract boolean	offerFirst(E e) Inserts the specified element at the front of this deque unless it would violate capacity restrictions.
abstract boolean	offerLast(E e) Inserts the specified element at the end of this deque unless it would violate capacity restrictions.
abstract 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.
abstract E	peekFirst() Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.
abstract E	peekLast() Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.
abstract 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.
abstract E	pollFirst() Retrieves and removes the first element of this deque, or returns null if this deque is empty.
abstract E	pollLast() Retrieves and removes the last element of this deque, or returns null if this deque is empty.
abstract E	pop() Pops an element from the stack represented by this deque.
abstract 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.
abstract E	remove() Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).
abstract boolean	remove(Object o) Removes the first occurrence of the specified element from this deque.
abstract E	removeFirst() Retrieves and removes the first element of this deque.
abstract boolean	removeFirstOccurrence(Object o) Removes the first occurrence of the specified element from this deque.
abstract E	removeLast() Retrieves and removes the last element of this deque.
abstract boolean	removeLastOccurrence(Object o) Removes the last occurrence of the specified element from this deque.
abstract int	size() Returns the number of elements in this deque.

Public Constructors

public LinkedBlockingDeque ()

Creates a LinkedBlockingDeque with a capacity of Integer.MAX_VALUE.

public LinkedBlockingDeque (int capacity)

Creates a LinkedBlockingDeque with the given (fixed) capacity.

Parameters

capacity	the capacity of this deque

Throws

IllegalArgumentException	if capacity is less than 1

public LinkedBlockingDeque (Collection<? extends E> c)

Creates a LinkedBlockingDeque 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

Public Methods

public 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	the element to add

Returns

• true (as specified by Collection.add(E))

Throws

IllegalStateException	if this deque is full
NullPointerException	if the specified element is null

public 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	the element to add

Throws

IllegalStateException	if this deque is full
NullPointerException

public 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	the element to add

Throws

IllegalStateException	if this deque is full
NullPointerException

public void clear ()

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

public 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 to be checked for containment in this deque

Returns

• true if this deque contains the specified element

public 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

• an iterator over the elements in this deque in reverse order

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	the collection to transfer elements into
maxElements	the maximum number of elements to transfer

Returns

• the number of elements transferred

Throws

UnsupportedOperationException
ClassCastException
NullPointerException
IllegalArgumentException

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	the collection to transfer elements into

Returns

• the number of elements transferred

Throws

UnsupportedOperationException
ClassCastException
NullPointerException
IllegalArgumentException

public 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

• the head of the queue represented by this deque

Throws

NoSuchElementException	if this deque is empty

public 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

• the head of this deque

Throws

NoSuchElementException

public 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

• the tail of this deque

Throws

NoSuchElementException

public 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

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

public 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	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 the element was added to this deque, else false

Throws

NullPointerException
InterruptedException

public 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	the element to add

Returns

• true if the element was added to this deque, else false

Throws

NullPointerException	if the specified element is null

public 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	the element to add

Returns

• true if the element was added to this deque, else false

Throws

NullPointerException

public 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	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

NullPointerException
InterruptedException

public 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	the element to add

Returns

• true if the element was added to this deque, else false

Throws

NullPointerException

public 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	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

NullPointerException
InterruptedException

public 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

• the head of this deque, or null if this deque is empty

public E peekFirst ()

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

Returns

• the head of this deque, or null if this deque is empty

public E peekLast ()

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

Returns

• the tail of this deque, or null if this deque is empty

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

Throws

InterruptedException

public 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 Deque.pollFirst().

Returns

• the head of this deque, or null if this deque is empty

public E pollFirst ()

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

Returns

• the head of this deque, or null if this deque is empty

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

Throws

InterruptedException

public 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	how long to wait before giving up, in units of unit
unit	a TimeUnit determining how to interpret the timeout parameter

Returns

• the tail of this deque, or null if the specified waiting time elapses before an element is available

Throws

InterruptedException

public E pollLast ()

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

Returns

• the tail of this deque, or null if this deque is empty

public 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

• the element at the front of this deque (which is the top of the stack represented by this deque)

Throws

NoSuchElementException

public 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	the element to push

Throws

IllegalStateException	if this deque is full
NullPointerException

public 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	the element to add

Throws

NullPointerException
InterruptedException

public void putFirst (E e)

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

Parameters

e	the element to add

Throws

NullPointerException
InterruptedException

public void putLast (E e)

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

Parameters

e	the element to add

Throws

NullPointerException
InterruptedException

public 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

• the remaining capacity

public 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

• the head of the queue represented by this deque

Throws

NoSuchElementException	if this deque is empty

public 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	element to be removed from this deque, if present

Returns

• true if this deque changed as a result of the call

public 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

• the head of this deque

Throws

NoSuchElementException

public 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	element to be removed from this deque, if present

Returns

• true if an element was removed as a result of this call

public 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

• the tail of this deque

Throws

NoSuchElementException

public 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	element to be removed from this deque, if present

Returns

• true if an element was removed as a result of this call

public int size ()

Returns the number of elements in this deque.

Returns

• the number of elements in this deque

public Spliterator<E> spliterator ()

Returns a Spliterator over the elements in this deque.

The returned spliterator is weakly consistent.

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

Returns

• a Spliterator over the elements in this deque

public 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

• the head of this deque

Throws

InterruptedException

public E takeFirst ()

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

Returns

• the head of this deque

Throws

InterruptedException

public E takeLast ()

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

Returns

• the tail of this deque

Throws

InterruptedException

public 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

• an array containing all of the elements in this deque

public 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	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

• 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

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

• a string representation of this collection