edu.emory.mathcs.backport.java.util.concurrent
Interface BlockingDeque

All Superinterfaces:

BlockingQueue, java.util.Collection, Deque, Queue

All Known Implementing Classes:

LinkedBlockingDeque

public interface BlockingDeque

extends BlockingQueue, Deque

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.

Since:

1.6

Author:

Doug Lea

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

addFirst

public 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. When using a capacity-restricted deque, it is generally preferable to use offerFirst.

Specified by:

addFirst in interface Deque

Parameters:

e - the element to add

Throws:

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

addLast

public 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. When using a capacity-restricted deque, it is generally preferable to use offerLast.

Specified by:

addLast in interface Deque

Parameters:

e - the element to add

Throws:

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

offerFirst

public 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. 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

Parameters:

e - the element to add

Returns:

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

Throws:

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

offerLast

public 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. 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

Parameters:

e - the element to add

Returns:

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

Throws:

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

putFirst

public void putFirst(java.lang.Object e)
              throws java.lang.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:

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

putLast

public void putLast(java.lang.Object e)
             throws java.lang.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:

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

offerFirst

public boolean offerFirst(java.lang.Object e,
                          long timeout,
                          TimeUnit unit)
                   throws java.lang.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:

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

offerLast

public boolean offerLast(java.lang.Object e,
                         long timeout,
                         TimeUnit unit)
                  throws java.lang.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:

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

takeFirst

public java.lang.Object takeFirst()
                           throws java.lang.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:

java.lang.InterruptedException - if interrupted while waiting

takeLast

public java.lang.Object takeLast()
                          throws java.lang.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:

java.lang.InterruptedException - if interrupted while waiting

pollFirst

public java.lang.Object pollFirst(long timeout,
                                  TimeUnit unit)
                           throws java.lang.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:

java.lang.InterruptedException - if interrupted while waiting

pollLast

public java.lang.Object pollLast(long timeout,
                                 TimeUnit unit)
                          throws java.lang.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:

java.lang.InterruptedException - if interrupted while waiting

removeFirstOccurrence

public boolean removeFirstOccurrence(java.lang.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

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:

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)

removeLastOccurrence

public boolean removeLastOccurrence(java.lang.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

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:

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)

add

public 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. 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

Parameters:

e - the element to add

Returns:

true (as specified by Collection.add(java.lang.Object))

Throws:

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

offer

public 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. When using a capacity-restricted deque, this method is generally preferable to the add(java.lang.Object) 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

Parameters:

e - the element to add

Returns:

true if the element was added to this queue, else false

Throws:

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

put

public void put(java.lang.Object e)
         throws java.lang.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

Parameters:

e - the element to add

Throws:

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

offer

public boolean offer(java.lang.Object e,
                     long timeout,
                     TimeUnit unit)
              throws java.lang.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

Parameters:

e - the element to add

timeout - how long to wait before giving up, in units of unit

unit - a TimeUnit determining how to interpret the timeout parameter

Returns:

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

Throws:

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

remove

public 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). 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

Returns:

the head of the queue represented by this deque

Throws:

NoSuchElementException - if this deque is empty

poll

public 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.

This method is equivalent to Deque.pollFirst().

Specified by:

poll in interface Queue

Returns:

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

take

public java.lang.Object take()
                      throws java.lang.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

Returns:

the head of this deque

Throws:

java.lang.InterruptedException - if interrupted while waiting

poll

public java.lang.Object poll(long timeout,
                             TimeUnit unit)
                      throws java.lang.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

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:

java.lang.InterruptedException - if interrupted while waiting

element

public 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). 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

Returns:

the head of this deque

Throws:

NoSuchElementException - if this deque is empty

peek

public 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.

This method is equivalent to peekFirst.

Specified by:

peek in interface Queue

Returns:

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

remove

public boolean remove(java.lang.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

Parameters:

o - element to be removed from this deque, if present

Returns:

true if this deque changed as a result of the call

Throws:

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)

contains

public boolean contains(java.lang.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

Parameters:

o - object to be checked for containment in this deque

Returns:

true if this deque contains the specified element

Throws:

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)

size

public int size()

Returns the number of elements in this deque.

Specified by:

size in interface java.util.Collection

Returns:

the number of elements in this deque

iterator

public java.util.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 java.util.Collection

Returns:

an iterator over the elements in this deque in proper sequence

push

public void push(java.lang.Object 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

Parameters:

e - the element to push

Throws:

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