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- Type Parameters:
- E- the type of elements held in this deque
 - All Superinterfaces:
- BlockingQueue<E>,- Collection<E>,- Deque<E>,- Iterable<E>,- Queue<E>
 - All Known Implementing Classes:
- LinkedBlockingDeque
 
 public interface BlockingDeque<E> extends BlockingQueue<E>, Deque<E> ADequethat 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.BlockingDequemethods 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 (eithernullorfalse, 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, aBlockingDequeis thread safe, does not permit null elements, and may (or may not) be capacity-constrained.A BlockingDequeimplementation may be used directly as a FIFOBlockingQueue. The methods inherited from theBlockingQueueinterface are precisely equivalent toBlockingDequemethods as indicated in the following table:Comparison of BlockingQueue and BlockingDeque methods BlockingQueueMethodEquivalent BlockingDequeMethodInsert 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 BlockingDequehappen-before actions subsequent to the access or removal of that element from theBlockingDequein another thread.This interface is a member of the Java Collections Framework. - Since:
- 1.6
 
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Method SummaryAll Methods Instance Methods Abstract Methods Modifier and Type Method Description booleanadd(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, returningtrueupon success and throwing anIllegalStateExceptionif no space is currently available.voidaddFirst(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 anIllegalStateExceptionif no space is currently available.voidaddLast(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 anIllegalStateExceptionif no space is currently available.booleancontains(Object o)Returnstrueif this deque contains the specified element.Eelement()Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque).Iterator<E>iterator()Returns an iterator over the elements in this deque in proper sequence.booleanoffer(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, returningtrueupon success andfalseif no space is currently available.booleanoffer(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.booleanofferFirst(E e)Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, returningtrueupon success andfalseif no space is currently available.booleanofferFirst(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.booleanofferLast(E e)Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, returningtrueupon success andfalseif no space is currently available.booleanofferLast(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.Epeek()Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returnsnullif this deque is empty.Epoll()Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returnsnullif this deque is empty.Epoll(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.EpollFirst(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.EpollLast(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.voidpush(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 anIllegalStateExceptionif no space is currently available.voidput(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.voidputFirst(E e)Inserts the specified element at the front of this deque, waiting if necessary for space to become available.voidputLast(E e)Inserts the specified element at the end of this deque, waiting if necessary for space to become available.Eremove()Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).booleanremove(Object o)Removes the first occurrence of the specified element from this deque.booleanremoveFirstOccurrence(Object o)Removes the first occurrence of the specified element from this deque.booleanremoveLastOccurrence(Object o)Removes the last occurrence of the specified element from this deque.intsize()Returns the number of elements in this deque.Etake()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.EtakeFirst()Retrieves and removes the first element of this deque, waiting if necessary until an element becomes available.EtakeLast()Retrieves and removes the last element of this deque, waiting if necessary until an element becomes available.- 
Methods declared in interface java.util.concurrent.BlockingQueuedrainTo, drainTo, remainingCapacity
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Methods declared in interface java.util.Collectionclear, containsAll, equals, hashCode, isEmpty, parallelStream, removeAll, removeIf, retainAll, spliterator, stream, toArray, toArray, toArray
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Methods declared in interface java.util.DequeaddAll, descendingIterator, getFirst, getLast, peekFirst, peekLast, pollFirst, pollLast, pop, removeFirst, removeLast
 
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Method Detail- 
addFirstvoid 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 anIllegalStateExceptionif no space is currently available. When using a capacity-restricted deque, it is generally preferable to useofferFirst.- Specified by:
- addFirstin interface- Deque<E>
- Parameters:
- e- the element to add
- Throws:
- IllegalStateException- if the element cannot be added at this time due to capacity restrictions
- 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
 
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addLastvoid 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 anIllegalStateExceptionif no space is currently available. When using a capacity-restricted deque, it is generally preferable to useofferLast.- Specified by:
- addLastin interface- Deque<E>
- Parameters:
- e- the element to add
- Throws:
- IllegalStateException- if the element cannot be added at this time due to capacity restrictions
- 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
 
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offerFirstboolean 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, returningtrueupon success andfalseif no space is currently available. When using a capacity-restricted deque, this method is generally preferable to theaddFirstmethod, which can fail to insert an element only by throwing an exception.- Specified by:
- offerFirstin interface- Deque<E>
- Parameters:
- e- the element to add
- Returns:
- trueif 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
 
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offerLastboolean 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, returningtrueupon success andfalseif no space is currently available. When using a capacity-restricted deque, this method is generally preferable to theaddLastmethod, which can fail to insert an element only by throwing an exception.- Specified by:
- offerLastin interface- Deque<E>
- Parameters:
- e- the element to add
- Returns:
- trueif 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
 
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putFirstvoid 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
 
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putLastvoid 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
 
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offerFirstboolean 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- TimeUnitdetermining how to interpret the- timeoutparameter
- Returns:
- trueif successful, or- falseif 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
 
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offerLastboolean 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- TimeUnitdetermining how to interpret the- timeoutparameter
- Returns:
- trueif successful, or- falseif 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
 
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takeFirstE 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
 
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takeLastE 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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pollFirstE 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- TimeUnitdetermining how to interpret the- timeoutparameter
- Returns:
- the head of this deque, or nullif the specified waiting time elapses before an element is available
- Throws:
- InterruptedException- if interrupted while waiting
 
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pollLastE 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- TimeUnitdetermining how to interpret the- timeoutparameter
- Returns:
- the tail of this deque, or nullif the specified waiting time elapses before an element is available
- Throws:
- InterruptedException- if interrupted while waiting
 
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removeFirstOccurrenceboolean 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 elementesuch thato.equals(e)(if such an element exists). Returnstrueif this deque contained the specified element (or equivalently, if this deque changed as a result of the call).- Specified by:
- removeFirstOccurrencein interface- Deque<E>
- Parameters:
- o- element to be removed from this deque, if present
- Returns:
- trueif 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)
 
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removeLastOccurrenceboolean 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 elementesuch thato.equals(e)(if such an element exists). Returnstrueif this deque contained the specified element (or equivalently, if this deque changed as a result of the call).- Specified by:
- removeLastOccurrencein interface- Deque<E>
- Parameters:
- o- element to be removed from this deque, if present
- Returns:
- trueif 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)
 
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addboolean 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, returningtrueupon success and throwing anIllegalStateExceptionif no space is currently available. When using a capacity-restricted deque, it is generally preferable to useoffer.This method is equivalent to addLast.- Specified by:
- addin interface- BlockingQueue<E>
- Specified by:
- addin interface- Collection<E>
- Specified by:
- addin interface- Deque<E>
- Specified by:
- addin interface- Queue<E>
- Parameters:
- e- the element to add
- Returns:
- true(as specified by- Collection.add(E))
- Throws:
- IllegalStateException- if the element cannot be added at this time due to capacity restrictions
- 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
 
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offerboolean 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, returningtrueupon success andfalseif no space is currently available. When using a capacity-restricted deque, this method is generally preferable to theadd(E)method, which can fail to insert an element only by throwing an exception.This method is equivalent to offerLast.- Specified by:
- offerin interface- BlockingQueue<E>
- Specified by:
- offerin interface- Deque<E>
- Specified by:
- offerin interface- Queue<E>
- Parameters:
- e- the element to add
- Returns:
- trueif the element was added to this queue, 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
 
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putvoid 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:
- putin interface- BlockingQueue<E>
- 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
 
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offerboolean 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:
- offerin interface- BlockingQueue<E>
- Parameters:
- e- the element to add
- timeout- how long to wait before giving up, in units of- unit
- unit- a- TimeUnitdetermining how to interpret the- timeoutparameter
- Returns:
- trueif the element was added to this deque, else- false
- 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
 
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removeE 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 frompoll()only in that it throws an exception if this deque is empty.This method is equivalent to removeFirst.
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pollE poll() Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returnsnullif this deque is empty.This method is equivalent to Deque.pollFirst().
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takeE 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:
- takein interface- BlockingQueue<E>
- Returns:
- the head of this deque
- Throws:
- InterruptedException- if interrupted while waiting
 
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pollE 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:
- pollin interface- BlockingQueue<E>
- Parameters:
- timeout- how long to wait before giving up, in units of- unit
- unit- a- TimeUnitdetermining how to interpret the- timeoutparameter
- Returns:
- the head of this deque, or nullif the specified waiting time elapses before an element is available
- Throws:
- InterruptedException- if interrupted while waiting
 
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elementE element() 
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peekE 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 returnsnullif this deque is empty.This method is equivalent to peekFirst.
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removeboolean 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 elementesuch thato.equals(e)(if such an element exists). Returnstrueif 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:
- removein interface- BlockingQueue<E>
- Specified by:
- removein interface- Collection<E>
- Specified by:
- removein interface- Deque<E>
- Parameters:
- o- element to be removed from this deque, if present
- Returns:
- trueif 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)
 
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containsboolean contains(Object o) Returnstrueif this deque contains the specified element. More formally, returnstrueif and only if this deque contains at least one elementesuch thato.equals(e).- Specified by:
- containsin interface- BlockingQueue<E>
- Specified by:
- containsin interface- Collection<E>
- Specified by:
- containsin interface- Deque<E>
- Parameters:
- o- object to be checked for containment in this deque
- Returns:
- trueif 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)
 
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sizeint size() Returns the number of elements in this deque.
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iteratorIterator<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).
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pushvoid 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 anIllegalStateExceptionif no space is currently available.This method is equivalent to addFirst.- Specified by:
- pushin interface- Deque<E>
- Parameters:
- e- the element to push
- Throws:
- IllegalStateException- if the element cannot be added at this time due to capacity restrictions
- 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
 
 
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