java.util.concurrent

Interface BlockingDeque<E>

All Superinterfaces:: BlockingQueue<E>, Collection<E>, Deque<E>, Iterable<E>, Queue<E>

Known Implementing Classes:: LinkedBlockingDeque<E>

public interface BlockingDeque<E>

extends BlockingQueue<E>, Deque<E>

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:

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:

`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 ../../../../technotes/guides/collections/index.html"> Java Collections Framework.

Since:: 1.6

Method Summary
`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.
`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.
`boolean`	`contains(Object o)` Returns `true` if this deque contains the specified element.
`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).
`Iterator`	`iterator()` Returns an iterator over the elements in this deque in proper sequence.
`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`	`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`	`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`	`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`	`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`	`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.
`void`	`push(E e)` Pushes an element onto the stack represented by this deque.
`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.
`E`	`remove()` Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).
`boolean`	`remove(Object o)` Removes the first occurrence of the specified element from this deque.
`boolean`	`removeFirstOccurrence(Object o)` Removes the first occurrence of the specified element from 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.
`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.

Methods inherited from interface java.util.concurrent.BlockingQueue<E>
`add`, `contains`, `drainTo`, `drainTo`, `offer`, `offer`, `poll`, `put`, `remainingCapacity`, `remove`, `take`

Methods inherited from interface java.util.Collection<E>
`T[] toArray`, `add`, `addAll`, `clear`, `contains`, `containsAll`, `equals`, `hashCode`, `isEmpty`, `iterator`, `remove`, `removeAll`, `retainAll`, `size`, `toArray`

Methods inherited from interface java.util.Deque<E>
`add`, `addFirst`, `addLast`, `contains`, `descendingIterator`, `element`, `getFirst`, `getLast`, `iterator`, `offer`, `offerFirst`, `offerLast`, `peek`, `peekFirst`, `peekLast`, `poll`, `pollFirst`, `pollLast`, `pop`, `push`, `remove`, `remove`, `removeFirst`, `removeFirstOccurrence`, `removeLast`, `removeLastOccurrence`, `size`

Methods inherited from interface java.lang.Iterable<E>
`iterator`

Methods inherited from interface java.util.Queue<E>
`add`, `element`, `offer`, `peek`, `poll`, `remove`

add

public 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.
Specified by:
add in interface BlockingQueue<E>
add in interface Queue<E>
add in interface Collection<E>
add in interface Deque<E>
Parameters:
e - the element to add
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

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.
Specified by:
addFirst in interface Deque<E>
Parameters:
e - the element to add
Throws:
IllegalStateException -
ClassCastException -
NullPointerException - if the specified element is null
IllegalArgumentException -

addLast

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.
Specified by:
addLast in interface Deque<E>
Parameters:
e - the element to add
Throws:
IllegalStateException -
ClassCastException -
NullPointerException - if the specified element is null
IllegalArgumentException -

contains

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).
Specified by:
contains in interface BlockingQueue<E>
contains in interface Collection<E>
contains in interface Deque<E>
Parameters:
o - object to be checked for containment in this deque
Returns:
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

public 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.
Specified by:
element in interface Queue<E>
element in interface Deque<E>
Returns:
the head of this deque
Throws:
NoSuchElementException - if this deque is empty

iterator

public Iterator 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).
Specified by:
iterator in interface Collection<E>
iterator in interface Iterable<E>
iterator in interface Deque<E>
Returns:
an iterator over the elements in this deque in proper sequence

offer

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.
Specified by:
offer in interface BlockingQueue<E>
offer in interface Queue<E>
offer in interface Deque<E>
Parameters:
e - the element to add
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

offer

public boolean offer(E e,
                     long timeout,
                     TimeUnit unit)
            throws InterruptedException

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.
Specified by:
offer in interface BlockingQueue<E>
Parameters:
e - the element to add
Returns:
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

offerFirst

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.
Specified by:
offerFirst in interface Deque<E>
Parameters:
e - the element to add
Throws:
ClassCastException -
NullPointerException - if the specified element is null
IllegalArgumentException -

offerFirst

public boolean offerFirst(E e,
                          long timeout,
                          TimeUnit unit)
            throws InterruptedException

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:
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

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.
Specified by:
offerLast in interface Deque<E>
Parameters:
e - the element to add
Throws:
ClassCastException -
NullPointerException - if the specified element is null
IllegalArgumentException -

offerLast

public boolean offerLast(E e,
                         long timeout,
                         TimeUnit unit)
            throws InterruptedException

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:
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

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.
Specified by:
peek in interface Queue<E>
peek in interface Deque<E>
Returns:
the head of this deque, or null if this deque is empty

poll

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 pollFirst().
Specified by:
poll in interface Queue<E>
poll in interface Deque<E>
Returns:
the head of this deque, or null if this deque is empty

poll

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

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.
Specified by:
poll in interface BlockingQueue<E>
Returns:
the head of this deque, or null if the specified waiting time elapses before an element is available
Throws:
InterruptedException - if interrupted while waiting

pollFirst

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

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 - if interrupted while waiting

pollLast

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

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 - if interrupted while waiting

push

public void push(E e)

Pushes an element onto the stack represented by this deque. In other words, inserts the element at the front of this deque unless it would violate capacity restrictions.
This method is equivalent to addFirst.
Specified by:
push in interface Deque<E>
Throws:
IllegalStateException -
ClassCastException -
NullPointerException - if the specified element is null
IllegalArgumentException -

put

public void put(E e)
            throws InterruptedException

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.
Specified by:
put in interface BlockingQueue<E>
Parameters:
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

public void putFirst(E e)
            throws InterruptedException

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:
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

public void putLast(E e)
            throws InterruptedException

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:
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

public 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.
Specified by:
remove in interface Queue<E>
remove in interface Deque<E>
Returns:
the head of the queue represented by this deque
Throws:
NoSuchElementException - if this deque is empty

remove

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.
Specified by:
remove in interface BlockingQueue<E>
remove in interface Collection<E>
remove in interface Deque<E>
Parameters:
o - element to be removed from this deque, if present
Returns:
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

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).
Specified by:
removeFirstOccurrence in interface Deque<E>
Parameters:
o - element to be removed from this deque, if present
Returns:
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

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).
Specified by:
removeLastOccurrence in interface Deque<E>
Parameters:
o - element to be removed from this deque, if present
Returns:
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

public int size()

Returns the number of elements in this deque.
Specified by:
size in interface Collection<E>
size in interface Deque<E>
Returns:
the number of elements in this deque

take

public E take()
            throws InterruptedException

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

takeFirst

public E takeFirst()
            throws InterruptedException

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 - if interrupted while waiting

takeLast

public E takeLast()
            throws InterruptedException

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 - if interrupted while waiting

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java.util.concurrent

Interface BlockingDeque<E>

Method Summary

Methods inherited from interface java.util.concurrent.BlockingQueue<E>

Methods inherited from interface java.util.Collection<E>

Methods inherited from interface java.util.Deque<E>

Methods inherited from interface java.lang.Iterable<E>

Methods inherited from interface java.util.Queue<E>

Method Details

add

addFirst

addLast

contains

element

iterator

offer

offer

offerFirst

offerFirst

offerLast

offerLast

peek

poll

poll

pollFirst

pollLast

push

put

putFirst

putLast

remove

remove

removeFirstOccurrence

removeLastOccurrence

size

take

takeFirst

takeLast