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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 happen-before actions subsequent to the access or removal of that element from the in another thread.
This interface is a member of the Java Collections Framework.
| Method Summary | |
boolean |
add(java.lang.Object 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(java.lang.Object 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(java.lang.Object 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(java.lang.Object o)
Returns true if this deque contains the specified element. |
java.lang.Object |
element()
Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque). |
java.util.Iterator |
iterator()
Returns an iterator over the elements in this deque in proper sequence. |
boolean |
offer(java.lang.Object 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(java.lang.Object 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(java.lang.Object 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(java.lang.Object 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(java.lang.Object 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(java.lang.Object 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. |
java.lang.Object |
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. |
java.lang.Object |
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. |
java.lang.Object |
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. |
java.lang.Object |
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. |
java.lang.Object |
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(java.lang.Object e)
Pushes an element onto the stack represented by this deque. |
void |
put(java.lang.Object 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(java.lang.Object e)
Inserts the specified element at the front of this deque, waiting if necessary for space to become available. |
void |
putLast(java.lang.Object e)
Inserts the specified element at the end of this deque, waiting if necessary for space to become available. |
java.lang.Object |
remove()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). |
boolean |
remove(java.lang.Object o)
Removes the first occurrence of the specified element from this deque. |
boolean |
removeFirstOccurrence(java.lang.Object o)
Removes the first occurrence of the specified element from this deque. |
boolean |
removeLastOccurrence(java.lang.Object o)
Removes the last occurrence of the specified element from this deque. |
int |
size()
Returns the number of elements in this deque. |
java.lang.Object |
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. |
java.lang.Object |
takeFirst()
Retrieves and removes the first element of this deque, waiting if necessary until an element becomes available. |
java.lang.Object |
takeLast()
Retrieves and removes the last element of this deque, waiting if necessary until an element becomes available. |
| Methods inherited from interface edu.emory.mathcs.backport.java.util.concurrent.BlockingQueue |
drainTo, drainTo, remainingCapacity |
| Methods inherited from interface java.util.Collection |
addAll, clear, containsAll, equals, hashCode, isEmpty, removeAll, retainAll, toArray, toArray |
| Methods inherited from interface edu.emory.mathcs.backport.java.util.Deque |
descendingIterator, getFirst, getLast, peekFirst, peekLast, pollFirst, pollLast, pop, removeFirst, removeLast |
| Method Detail |
public void addFirst(java.lang.Object e)
offerFirst.
addFirst in interface Dequee - the element to add
java.lang.IllegalStateException - if the element cannot be added at this
time due to capacity restrictions
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this dequepublic void addLast(java.lang.Object e)
offerLast.
addLast in interface Dequee - the element to add
java.lang.IllegalStateException - if the element cannot be added at this
time due to capacity restrictions
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this dequepublic boolean offerFirst(java.lang.Object e)
addFirst method, which can
fail to insert an element only by throwing an exception.
offerFirst in interface Dequee - the element to add
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this dequepublic boolean offerLast(java.lang.Object e)
addLast method, which can
fail to insert an element only by throwing an exception.
offerLast in interface Dequee - the element to add
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this deque
public void putFirst(java.lang.Object e)
throws java.lang.InterruptedException
e - the element to add
java.lang.InterruptedException - if interrupted while waiting
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this deque
public void putLast(java.lang.Object e)
throws java.lang.InterruptedException
e - the element to add
java.lang.InterruptedException - if interrupted while waiting
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this deque
public boolean offerFirst(java.lang.Object e,
long timeout,
TimeUnit unit)
throws java.lang.InterruptedException
e - the element to addtimeout - how long to wait before giving up, in units of
unitunit - a TimeUnit determining how to interpret the
timeout parameter
java.lang.InterruptedException - if interrupted while waiting
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this deque
public boolean offerLast(java.lang.Object e,
long timeout,
TimeUnit unit)
throws java.lang.InterruptedException
e - the element to addtimeout - how long to wait before giving up, in units of
unitunit - a TimeUnit determining how to interpret the
timeout parameter
java.lang.InterruptedException - if interrupted while waiting
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this deque
public java.lang.Object takeFirst()
throws java.lang.InterruptedException
java.lang.InterruptedException - if interrupted while waiting
public java.lang.Object takeLast()
throws java.lang.InterruptedException
java.lang.InterruptedException - if interrupted while waiting
public java.lang.Object pollFirst(long timeout,
TimeUnit unit)
throws java.lang.InterruptedException
timeout - how long to wait before giving up, in units of
unitunit - a TimeUnit determining how to interpret the
timeout parameter
java.lang.InterruptedException - if interrupted while waiting
public java.lang.Object pollLast(long timeout,
TimeUnit unit)
throws java.lang.InterruptedException
timeout - how long to wait before giving up, in units of
unitunit - a TimeUnit determining how to interpret the
timeout parameter
java.lang.InterruptedException - if interrupted while waitingpublic boolean removeFirstOccurrence(java.lang.Object o)
removeFirstOccurrence in interface Dequeo - element to be removed from this deque, if present
java.lang.ClassCastException - if the class of the specified element
is incompatible with this deque (optional)
java.lang.NullPointerException - if the specified element is null (optional)public boolean removeLastOccurrence(java.lang.Object o)
removeLastOccurrence in interface Dequeo - element to be removed from this deque, if present
java.lang.ClassCastException - if the class of the specified element
is incompatible with this deque (optional)
java.lang.NullPointerException - if the specified element is null (optional)public boolean add(java.lang.Object e)
offer.
This method is equivalent to addLast.
add in interface BlockingQueuee - the element to add
Collection.add(java.lang.Object))
java.lang.IllegalStateException - if the element cannot be added at this
time due to capacity restrictions
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this dequepublic boolean offer(java.lang.Object e)
add(java.lang.Object) method, which can fail to
insert an element only by throwing an exception.
This method is equivalent to offerLast.
offer in interface BlockingQueuee - the element to add
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this deque
public void put(java.lang.Object e)
throws java.lang.InterruptedException
This method is equivalent to putLast.
put in interface BlockingQueuee - the element to add
java.lang.InterruptedException - if interrupted while waiting
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this deque
public boolean offer(java.lang.Object e,
long timeout,
TimeUnit unit)
throws java.lang.InterruptedException
This method is equivalent to
offerLast.
offer in interface BlockingQueuee - the element to addtimeout - how long to wait before giving up, in units of
unitunit - a TimeUnit determining how to interpret the
timeout parameter
java.lang.InterruptedException - if interrupted while waiting
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this dequepublic java.lang.Object remove()
poll only in that it
throws an exception if this deque is empty.
This method is equivalent to removeFirst.
remove in interface QueueNoSuchElementException - if this deque is emptypublic java.lang.Object poll()
This method is equivalent to Deque.pollFirst().
poll in interface Queue
public java.lang.Object take()
throws java.lang.InterruptedException
This method is equivalent to takeFirst.
take in interface BlockingQueuejava.lang.InterruptedException - if interrupted while waiting
public java.lang.Object poll(long timeout,
TimeUnit unit)
throws java.lang.InterruptedException
This method is equivalent to
pollFirst.
poll in interface BlockingQueuetimeout - how long to wait before giving up, in units of
unitunit - a TimeUnit determining how to interpret the
timeout parameter
java.lang.InterruptedException - if interrupted while waitingpublic java.lang.Object element()
peek only in that it throws an
exception if this deque is empty.
This method is equivalent to getFirst.
element in interface QueueNoSuchElementException - if this deque is emptypublic java.lang.Object peek()
This method is equivalent to peekFirst.
peek in interface Queuepublic boolean remove(java.lang.Object o)
This method is equivalent to
removeFirstOccurrence.
remove in interface BlockingQueueo - element to be removed from this deque, if present
java.lang.ClassCastException - if the class of the specified element
is incompatible with this deque (optional)
java.lang.NullPointerException - if the specified element is null (optional)public boolean contains(java.lang.Object o)
contains in interface BlockingQueueo - object to be checked for containment in this deque
java.lang.ClassCastException - if the class of the specified element
is incompatible with this deque (optional)
java.lang.NullPointerException - if the specified element is null (optional)public int size()
size in interface java.util.Collectionpublic java.util.Iterator iterator()
iterator in interface java.util.Collectionpublic void push(java.lang.Object e)
This method is equivalent to addFirst.
push in interface Dequee - the element to push
java.lang.IllegalStateException - if the element cannot be added at this
time due to capacity restrictions
java.lang.ClassCastException - if the class of the specified element
prevents it from being added to this deque
java.lang.NullPointerException - if the specified element is null
java.lang.IllegalArgumentException - if some property of the specified
element prevents it from being added to this deque
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