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BlockingDeque

public interface BlockingDeque
implements BlockingQueue<E>, Deque<E>

java.util.concurrent.BlockingDeque<E>
Known Indirect Subclasses


A Deque that additionally supports blocking operations that wait for the deque to become non-empty when retrieving an element, and wait for space to become available in the deque when storing an element.

BlockingDeque methods come in four forms, with different ways of handling operations that cannot be satisfied immediately, but may be satisfied at some point in the future: one throws an exception, the second returns a special value (either null or false, depending on the operation), the third blocks the current thread indefinitely until the operation can succeed, and the fourth blocks for only a given maximum time limit before giving up. These methods are summarized in the following table:

Summary of BlockingDeque methods
First Element (Head)
Throws exception Special value Blocks Times out
Insert addFirst(e) offerFirst(e) putFirst(e) offerFirst(e, time, unit)
Remove removeFirst() pollFirst() takeFirst() pollFirst(time, unit)
Examine getFirst() peekFirst() not applicable not applicable
Last Element (Tail)
Throws exception Special value Blocks Times out
Insert addLast(e) offerLast(e) putLast(e) offerLast(e, time, unit)
Remove removeLast() pollLast() takeLast() pollLast(time, unit)
Examine getLast() peekLast() not applicable not applicable

Like any BlockingQueue, a BlockingDeque is thread safe, does not permit null elements, and may (or may not) be capacity-constrained.

A BlockingDeque implementation may be used directly as a FIFO BlockingQueue. The methods inherited from the BlockingQueue interface are precisely equivalent to BlockingDeque methods as indicated in the following table:

Comparison of BlockingQueue and BlockingDeque methods
BlockingQueue Method Equivalent BlockingDeque Method
Insert
add(e) addLast(e)
offer(e) offerLast(e)
put(e) putLast(e)
offer(e, time, unit) offerLast(e, time, unit)
Remove
remove() removeFirst()
poll() pollFirst()
take() takeFirst()
poll(time, unit) pollFirst(time, unit)
Examine
element() getFirst()
peek() peekFirst()

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a BlockingDeque happen-before actions subsequent to the access or removal of that element from the BlockingDeque in another thread.

This interface is a member of the Java Collections Framework.

Summary

Public methods

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.

Inherited methods

From interface java.util.concurrent.BlockingQueue
From interface java.util.Deque
From interface java.util.Queue
From interface java.util.Collection
From interface java.lang.Iterable

Public methods

add

Added in API level 9
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. When using a capacity-restricted deque, it is generally preferable to use offer.

This method is equivalent to addLast.

Parameters
e E: the element to add
Returns
boolean true (as specified by add(E))
Throws
IllegalStateException
ClassCastException if the class of the specified element prevents it from being added to this deque
NullPointerException if the specified element is null
IllegalArgumentException if some property of the specified element prevents it from being added to this deque

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
ClassCastException
NullPointerException if the specified element is null
IllegalArgumentException

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
ClassCastException
NullPointerException if the specified element is null
IllegalArgumentException

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
Throws
ClassCastException if the class of the specified element is incompatible with this deque (optional)
NullPointerException if the specified element is null (optional)

element

Added in API level 9
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). 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 this deque
Throws
NoSuchElementException if this deque is empty

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).

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
InterruptedException
ClassCastException if the class of the specified element prevents it from being added to this deque
NullPointerException if the specified element is null
IllegalArgumentException if some property of the specified element prevents it from being added to this deque

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
ClassCastException if the class of the specified element prevents it from being added to this deque
NullPointerException if the specified element is null
IllegalArgumentException if some property of the specified element prevents it from being added to this deque

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
ClassCastException
NullPointerException if the specified element is null
IllegalArgumentException

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
InterruptedException if interrupted while waiting
ClassCastException if the class of the specified element prevents it from being added to this deque
NullPointerException if the specified element is null
IllegalArgumentException if some property of the specified element prevents it from being added to this deque

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
ClassCastException
NullPointerException if the specified element is null
IllegalArgumentException

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
InterruptedException if interrupted while waiting
ClassCastException if the class of the specified element prevents it from being added to this deque
NullPointerException if the specified element is null
IllegalArgumentException if some property of the specified element prevents it from being added to this deque

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

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 if interrupted while waiting

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 (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 if interrupted while waiting

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 if interrupted while waiting

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
ClassCastException
NullPointerException if the specified element is null
IllegalArgumentException

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
InterruptedException
ClassCastException if the class of the specified element prevents it from being added to this deque
NullPointerException if the specified element is null
IllegalArgumentException if some property of the specified element prevents it from being added to this deque

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
InterruptedException if interrupted while waiting
ClassCastException if the class of the specified element prevents it from being added to this deque
NullPointerException if the specified element is null
IllegalArgumentException if some property of the specified element prevents it from being added to this deque

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
InterruptedException if interrupted while waiting
ClassCastException if the class of the specified element prevents it from being added to this deque
NullPointerException if the specified element is null
IllegalArgumentException if some property of the specified element prevents it from being added to this deque

remove

Added in API level 9
E remove ()

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of 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
Throws
ClassCastException if the class of the specified element is incompatible with this deque (optional)
NullPointerException if the specified element is null (optional)

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
Throws
ClassCastException if the class of the specified element is incompatible with this deque (optional)
NullPointerException if the specified element is null (optional)

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
Throws
ClassCastException if the class of the specified element is incompatible with this deque (optional)
NullPointerException if the specified element is null (optional)

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

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 if interrupted while waiting

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 if interrupted while waiting

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 if interrupted while waiting
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