- Type Parameters:
E- the type of elements held in this deque
- All Implemented Interfaces:
Serializable,Cloneable,Iterable<E>,Collection<E>,Deque<E>,Queue<E>,SequencedCollection<E>
Deque interface. Array
deques have no capacity restrictions; they grow as necessary to support
usage. They are not thread-safe; in the absence of external
synchronization, they do not support concurrent access by multiple threads.
Null elements are prohibited. This class is likely to be faster than
Stack when used as a stack, and faster than LinkedList
when used as a queue.
Most ArrayDeque operations run in amortized constant time.
Exceptions include
remove,
removeFirstOccurrence,
removeLastOccurrence,
contains,
iterator.remove(),
and the bulk operations, all of which run in linear time.
The iterators returned by this class's iterator
method are fail-fast: If the deque is modified at any time after
the iterator is created, in any way except through the iterator's own
remove method, the iterator will generally throw a ConcurrentModificationException. Thus, in the face of concurrent
modification, the iterator fails quickly and cleanly, rather than risking
arbitrary, non-deterministic behavior at an undetermined time in the
future.
Note that the fail-fast behavior of an iterator cannot be guaranteed
as it is, generally speaking, impossible to make any hard guarantees in the
presence of unsynchronized concurrent modification. Fail-fast iterators
throw ConcurrentModificationException on a best-effort basis.
Therefore, it would be wrong to write a program that depended on this
exception for its correctness: the fail-fast behavior of iterators
should be used only to detect bugs.
This class and its iterator implement all of the optional methods of the
Collection, SequencedCollection, and Iterator interfaces.
This class is a member of the Java Collections Framework.
- Since:
- 1.6
- See Also:
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Constructor Summary
ConstructorsConstructorDescriptionConstructs an empty array deque with an initial capacity sufficient to hold 16 elements.ArrayDeque(int numElements) Constructs an empty array deque with an initial capacity sufficient to hold the specified number of elements.ArrayDeque(Collection<? extends E> c) Constructs a deque containing the elements of the specified collection, in the order they are returned by the collection's iterator. -
Method Summary
Modifier and TypeMethodDescriptionbooleanInserts the specified element at the end of this deque.booleanaddAll(Collection<? extends E> c) Adds all of the elements in the specified collection at the end of this deque, as if by callingaddLast(E)on each one, in the order that they are returned by the collection's iterator.voidInserts the specified element at the front of this deque.voidInserts the specified element at the end of this deque.voidclear()Removes all of the elements from this deque.clone()Returns a copy of this deque.booleanReturnstrueif this deque contains the specified element.Returns an iterator over the elements in this deque in reverse sequential order.element()Retrieves, but does not remove, the head of the queue represented by this deque.voidPerforms the given action for each element of theIterableuntil all elements have been processed or the action throws an exception.getFirst()Retrieves, but does not remove, the first element of this deque.getLast()Retrieves, but does not remove, the last element of this deque.booleanisEmpty()Returnstrueif this deque contains no elements.iterator()Returns an iterator over the elements in this deque.booleanInserts the specified element at the end of this deque.booleanofferFirst(E e) Inserts the specified element at the front of this deque.booleanInserts the specified element at the end of this deque.peek()Retrieves, but does not remove, the head of the queue represented by this deque, or returnsnullif this deque is empty.Retrieves, but does not remove, the first element of this deque, or returnsnullif this deque is empty.peekLast()Retrieves, but does not remove, the last element of this deque, or returnsnullif this deque is empty.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.Retrieves and removes the first element of this deque, or returnsnullif this deque is empty.pollLast()Retrieves and removes the last element of this deque, or returnsnullif this deque is empty.pop()Pops an element from the stack represented by this deque.voidPushes an element onto the stack represented by this deque.remove()Retrieves and removes the head of the queue represented by this deque.booleanRemoves a single instance of the specified element from this deque.booleanremoveAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation).Retrieves and removes the first element of this deque.booleanRemoves the first occurrence of the specified element in this deque (when traversing the deque from head to tail).booleanRemoves all of the elements of this collection that satisfy the given predicate.Retrieves and removes the last element of this deque.booleanRemoves the last occurrence of the specified element in this deque (when traversing the deque from head to tail).booleanretainAll(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation).intsize()Returns the number of elements in this deque.Creates a late-binding and fail-fastSpliteratorover the elements in this deque.Object[]toArray()Returns an array containing all of the elements in this deque in proper sequence (from first to last element).<T> T[]toArray(T[] a) Returns an array containing all of the elements in this deque in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.Methods declared in class java.util.AbstractCollection
containsAll, toStringMethods declared in class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitMethods declared in interface java.util.Collection
containsAll, equals, hashCode, parallelStream, stream, toArray
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Constructor Details
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ArrayDeque
public ArrayDeque()Constructs an empty array deque with an initial capacity sufficient to hold 16 elements. -
ArrayDeque
public ArrayDeque(int numElements) Constructs an empty array deque with an initial capacity sufficient to hold the specified number of elements.- Parameters:
numElements- lower bound on initial capacity of the deque
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ArrayDeque
Constructs a deque containing the elements of the specified collection, in the order they are returned by the collection's iterator. (The first element returned by the collection's iterator becomes the first element, or front of the deque.)- Parameters:
c- the collection whose elements are to be placed into the deque- Throws:
NullPointerException- if the specified collection is null
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Method Details
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addFirst
Inserts the specified element at the front of this deque.- Specified by:
addFirstin interfaceDeque<E>- Specified by:
addFirstin interfaceSequencedCollection<E>- Parameters:
e- the element to add- Throws:
NullPointerException- if the specified element is null
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addLast
Inserts the specified element at the end of this deque.This method is equivalent to
add(E).- Specified by:
addLastin interfaceDeque<E>- Specified by:
addLastin interfaceSequencedCollection<E>- Parameters:
e- the element to add- Throws:
NullPointerException- if the specified element is null
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addAll
Adds all of the elements in the specified collection at the end of this deque, as if by callingaddLast(E)on each one, in the order that they are returned by the collection's iterator.- Specified by:
addAllin interfaceCollection<E>- Specified by:
addAllin interfaceDeque<E>- Overrides:
addAllin classAbstractCollection<E>- Parameters:
c- the elements to be inserted into this deque- Returns:
trueif this deque changed as a result of the call- Throws:
NullPointerException- if the specified collection or any of its elements are null- See Also:
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offerFirst
Inserts the specified element at the front of this deque.- Specified by:
offerFirstin interfaceDeque<E>- Parameters:
e- the element to add- Returns:
true(as specified byDeque.offerFirst(E))- Throws:
NullPointerException- if the specified element is null
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offerLast
Inserts the specified element at the end of this deque.- Specified by:
offerLastin interfaceDeque<E>- Parameters:
e- the element to add- Returns:
true(as specified byDeque.offerLast(E))- Throws:
NullPointerException- if the specified element is null
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removeFirst
Description copied from interface:DequeRetrieves and removes the first element of this deque. This method differs frompollFirstonly in that it throws an exception if this deque is empty.- Specified by:
removeFirstin interfaceDeque<E>- Specified by:
removeFirstin interfaceSequencedCollection<E>- Returns:
- the head of this deque
- Throws:
NoSuchElementException- if this deque is empty
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removeLast
Description copied from interface:DequeRetrieves and removes the last element of this deque. This method differs frompollLastonly in that it throws an exception if this deque is empty.- Specified by:
removeLastin interfaceDeque<E>- Specified by:
removeLastin interfaceSequencedCollection<E>- Returns:
- the tail of this deque
- Throws:
NoSuchElementException- if this deque is empty
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pollFirst
Description copied from interface:DequeRetrieves and removes the first element of this deque, or returnsnullif this deque is empty. -
pollLast
Description copied from interface:DequeRetrieves and removes the last element of this deque, or returnsnullif this deque is empty. -
getFirst
Description copied from interface:DequeRetrieves, but does not remove, the first element of this deque. This method differs frompeekFirstonly in that it throws an exception if this deque is empty.- Specified by:
getFirstin interfaceDeque<E>- Specified by:
getFirstin interfaceSequencedCollection<E>- Returns:
- the head of this deque
- Throws:
NoSuchElementException- if this deque is empty
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getLast
Description copied from interface:DequeRetrieves, but does not remove, the last element of this deque. This method differs frompeekLastonly in that it throws an exception if this deque is empty.- Specified by:
getLastin interfaceDeque<E>- Specified by:
getLastin interfaceSequencedCollection<E>- Returns:
- the tail of this deque
- Throws:
NoSuchElementException- if this deque is empty
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peekFirst
Description copied from interface:DequeRetrieves, but does not remove, the first element of this deque, or returnsnullif this deque is empty. -
peekLast
Description copied from interface:DequeRetrieves, but does not remove, the last element of this deque, or returnsnullif this deque is empty. -
removeFirstOccurrence
Removes the first occurrence of the specified element in this deque (when traversing the deque from head to tail). 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 interfaceDeque<E>- Parameters:
o- element to be removed from this deque, if present- Returns:
trueif the deque contained the specified element
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removeLastOccurrence
Removes the last occurrence of the specified element in this deque (when traversing the deque from head to tail). 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 interfaceDeque<E>- Parameters:
o- element to be removed from this deque, if present- Returns:
trueif the deque contained the specified element
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add
Inserts the specified element at the end of this deque.This method is equivalent to
addLast(E).- Specified by:
addin interfaceCollection<E>- Specified by:
addin interfaceDeque<E>- Specified by:
addin interfaceQueue<E>- Overrides:
addin classAbstractCollection<E>- Parameters:
e- the element to add- Returns:
true(as specified byCollection.add(E))- Throws:
NullPointerException- if the specified element is null
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offer
Inserts the specified element at the end of this deque.This method is equivalent to
offerLast(E).- Specified by:
offerin interfaceDeque<E>- Specified by:
offerin interfaceQueue<E>- Parameters:
e- the element to add- Returns:
true(as specified byQueue.offer(E))- Throws:
NullPointerException- if the specified element is null
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remove
Retrieves and removes the head of the queue represented by this deque. This method differs frompoll()only in that it throws an exception if this deque is empty.This method is equivalent to
removeFirst(). -
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
pollFirst(). -
element
Retrieves, but does not remove, the head of the queue represented by this deque. This method differs frompeekonly in that it throws an exception if this deque is empty.This method is equivalent to
getFirst(). -
peek
Retrieves, but does not remove, the head of the queue represented by this deque, or returnsnullif this deque is empty.This method is equivalent to
peekFirst(). -
push
Pushes an element onto the stack represented by this deque. In other words, inserts the element at the front of this deque.This method is equivalent to
addFirst(E).- Specified by:
pushin interfaceDeque<E>- Parameters:
e- the element to push- Throws:
NullPointerException- if the specified element is null
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pop
Pops an element from the stack represented by this deque. In other words, removes and returns the first element of this deque.This method is equivalent to
removeFirst().- Specified by:
popin interfaceDeque<E>- Returns:
- the element at the front of this deque (which is the top of the stack represented by this deque)
- Throws:
NoSuchElementException- if this deque is empty
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size
public int size()Returns the number of elements in this deque. -
isEmpty
public boolean isEmpty()Returnstrueif this deque contains no elements.- Specified by:
isEmptyin interfaceCollection<E>- Overrides:
isEmptyin classAbstractCollection<E>- Returns:
trueif this deque contains no elements
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iterator
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descendingIterator
Description copied from interface:DequeReturns an iterator over the elements in this deque in reverse sequential order. The elements will be returned in order from last (tail) to first (head).- Specified by:
descendingIteratorin interfaceDeque<E>- Returns:
- an iterator over the elements in this deque in reverse sequence
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spliterator
Creates a late-binding and fail-fastSpliteratorover the elements in this deque.The
SpliteratorreportsSpliterator.SIZED,Spliterator.SUBSIZED,Spliterator.ORDERED, andSpliterator.NONNULL. Overriding implementations should document the reporting of additional characteristic values.- Specified by:
spliteratorin interfaceCollection<E>- Specified by:
spliteratorin interfaceIterable<E>- Returns:
- a
Spliteratorover the elements in this deque - Since:
- 1.8
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forEach
Description copied from interface:IterablePerforms the given action for each element of theIterableuntil all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
- Specified by:
forEachin interfaceIterable<E>- Parameters:
action- The action to be performed for each element- Throws:
NullPointerException- if the specified action is null
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removeIf
Description copied from interface:CollectionRemoves all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.- Specified by:
removeIfin interfaceCollection<E>- Parameters:
filter- a predicate which returnstruefor elements to be removed- Returns:
trueif any elements were removed- Throws:
NullPointerException- if the specified filter is null
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removeAll
Description copied from class:AbstractCollectionRemoves all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.- Specified by:
removeAllin interfaceCollection<E>- Overrides:
removeAllin classAbstractCollection<E>- Parameters:
c- collection containing elements to be removed from this collection- Returns:
trueif this collection changed as a result of the call- Throws:
NullPointerException- if this collection contains one or more null elements and the specified collection does not support null elements (optional) or if the specified collection is null- See Also:
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retainAll
Description copied from class:AbstractCollectionRetains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.- Specified by:
retainAllin interfaceCollection<E>- Overrides:
retainAllin classAbstractCollection<E>- Parameters:
c- collection containing elements to be retained in this collection- Returns:
trueif this collection changed as a result of the call- Throws:
NullPointerException- if this collection contains one or more null elements and the specified collection does not permit null elements (optional) or if the specified collection is null- See Also:
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contains
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 interfaceCollection<E>- Specified by:
containsin interfaceDeque<E>- Overrides:
containsin classAbstractCollection<E>- Parameters:
o- object to be checked for containment in this deque- Returns:
trueif this deque contains the specified element
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remove
Removes a single instance 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(Object).- Specified by:
removein interfaceCollection<E>- Specified by:
removein interfaceDeque<E>- Overrides:
removein classAbstractCollection<E>- Parameters:
o- element to be removed from this deque, if present- Returns:
trueif this deque contained the specified element
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clear
public void clear()Removes all of the elements from this deque. The deque will be empty after this call returns.- Specified by:
clearin interfaceCollection<E>- Overrides:
clearin classAbstractCollection<E>
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toArray
Returns an array containing all of the elements in this deque in proper sequence (from first to last element).The returned array will be "safe" in that no references to it are maintained by this deque. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
- Specified by:
toArrayin interfaceCollection<E>- Overrides:
toArrayin classAbstractCollection<E>- Returns:
- an array containing all of the elements in this deque
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toArray
public <T> T[] toArray(T[] a) Returns an array containing all of the elements in this deque in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. If the deque fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this deque.If this deque fits in the specified array with room to spare (i.e., the array has more elements than this deque), the element in the array immediately following the end of the deque is set to
null.Like the
toArray()method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.Suppose
xis a deque known to contain only strings. The following code can be used to dump the deque into a newly allocated array ofString:
Note thatString[] y = x.toArray(new String[0]);toArray(new Object[0])is identical in function totoArray().- Specified by:
toArrayin interfaceCollection<E>- Overrides:
toArrayin classAbstractCollection<E>- Type Parameters:
T- the component type of the array to contain the collection- Parameters:
a- the array into which the elements of the deque are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose- Returns:
- an array containing all of the elements in this deque
- Throws:
ArrayStoreException- if the runtime type of the specified array is not a supertype of the runtime type of every element in this dequeNullPointerException- if the specified array is null
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clone
Returns a copy of this deque.
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