E - the type of elements held in this collectionpublic class ArrayDeque<E> extends AbstractCollection<E> implements Deque<E>, Cloneable, Serializable
Resizable-array implementation of the 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 and Iterator interfaces.
This class is a member of the Java Collections Framework.
public ArrayDeque()
Constructs an empty array deque with an initial capacity sufficient to hold 16 elements.
public ArrayDeque(int numElements)
Constructs an empty array deque with an initial capacity sufficient to hold the specified number of elements.
numElements - lower bound on initial capacity of the dequepublic 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. (The first element returned by the collection's iterator becomes the first element, or front of the deque.)
c - the collection whose elements are to be placed into the dequeNullPointerException - if the specified collection is nullpublic void addFirst(E e)
Inserts the specified element at the front of this deque.
addFirst in interface Deque<E>
e - the element to addNullPointerException - if the specified element is nullpublic void addLast(E e)
Inserts the specified element at the end of this deque.
This method is equivalent to add(E).
addLast in interface Deque<E>
e - the element to addNullPointerException - if the specified element is nullpublic boolean offerFirst(E e)
Inserts the specified element at the front of this deque.
offerFirst in interface Deque<E>
e - the element to addtrue (as specified by Deque.offerFirst(E))NullPointerException - if the specified element is nullpublic boolean offerLast(E e)
Inserts the specified element at the end of this deque.
offerLast in interface Deque<E>
e - the element to addtrue (as specified by Deque.offerLast(E))NullPointerException - if the specified element is nullpublic E removeFirst()
Description copied from interface: Deque
Retrieves and removes the first element of this deque. This method differs from pollFirst only in that it throws an exception if this deque is empty.
removeFirst in interface Deque<E>
NoSuchElementException - if this deque is emptypublic E removeLast()
Description copied from interface: Deque
Retrieves and removes the last element of this deque. This method differs from pollLast only in that it throws an exception if this deque is empty.
removeLast in interface Deque<E>
NoSuchElementException - if this deque is emptypublic E pollFirst()
Description copied from interface: Deque
Retrieves and removes the first element of this deque, or returns null if this deque is empty.
pollFirst in interface Deque<E>
null if this deque is emptypublic E pollLast()
Description copied from interface: Deque
Retrieves and removes the last element of this deque, or returns null if this deque is empty.
pollLast in interface Deque<E>
null if this deque is emptypublic E getFirst()
Description copied from interface: Deque
Retrieves, but does not remove, the first element of this deque. This method differs from peekFirst only in that it throws an exception if this deque is empty.
getFirst in interface Deque<E>
NoSuchElementException - if this deque is emptypublic E getLast()
Description copied from interface: Deque
Retrieves, but does not remove, the last element of this deque. This method differs from peekLast only in that it throws an exception if this deque is empty.
getLast in interface Deque<E>
NoSuchElementException - if this deque is emptypublic E peekFirst()
Description copied from interface: Deque
Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.
peekFirst in interface Deque<E>
null if this deque is emptypublic E peekLast()
Description copied from interface: Deque
Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.
peekLast in interface Deque<E>
null if this deque is emptypublic boolean removeFirstOccurrence(Object o)
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 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).
removeFirstOccurrence in interface Deque<E>
o - element to be removed from this deque, if presenttrue if the deque contained the specified elementpublic boolean removeLastOccurrence(Object o)
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 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).
removeLastOccurrence in interface Deque<E>
o - element to be removed from this deque, if presenttrue if the deque contained the specified elementpublic boolean add(E e)
Inserts the specified element at the end of this deque.
This method is equivalent to addLast(E).
add in interface Collection<E>
add in interface Deque<E>
add in interface Queue<E>
add in class AbstractCollection<E>
e - the element to addtrue (as specified by Collection.add(E))NullPointerException - if the specified element is nullpublic boolean offer(E e)
Inserts the specified element at the end of this deque.
This method is equivalent to offerLast(E).
offer in interface Deque<E>
offer in interface Queue<E>
e - the element to addtrue (as specified by Queue.offer(E))NullPointerException - if the specified element is nullpublic E remove()
Retrieves and removes the head of the queue represented by 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().
remove in interface Deque<E>
remove in interface Queue<E>
NoSuchElementException - if this deque is emptypublic E poll()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.
This method is equivalent to pollFirst().
poll in interface Deque<E>
poll in interface Queue<E>
null if this deque is emptypublic E element()
Retrieves, but does not remove, the head of the queue represented by 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().
element in interface Deque<E>
element in interface Queue<E>
NoSuchElementException - if this deque is emptypublic E peek()
Retrieves, but does not remove, the head of the queue represented by this deque, or returns null if this deque is empty.
This method is equivalent to peekFirst().
peek in interface Deque<E>
peek in interface Queue<E>
null if this deque is emptypublic void push(E e)
Pushes an element onto the stack represented by this deque. In other words, inserts the element at the front of this deque.
This method is equivalent to addFirst(E).
push in interface Deque<E>
e - the element to pushNullPointerException - if the specified element is nullpublic E 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().
pop in interface Deque<E>
NoSuchElementException - if this deque is emptypublic int size()
Returns the number of elements in this deque.
size in interface Collection<E>
size in interface Deque<E>
size in class AbstractCollection<E>
public boolean isEmpty()
Returns true if this deque contains no elements.
isEmpty in interface Collection<E>
isEmpty in class AbstractCollection<E>
true if this deque contains no elementspublic Iterator<E> iterator()
Returns an iterator over the elements in this deque. The elements will be ordered from first (head) to last (tail). This is the same order that elements would be dequeued (via successive calls to remove() or popped (via successive calls to pop()).
iterator in interface Iterable<E>
iterator in interface Collection<E>
iterator in interface Deque<E>
iterator in class AbstractCollection<E>
public Iterator<E> descendingIterator()
Description copied from interface: Deque
Returns 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).
descendingIterator in interface Deque<E>
public boolean contains(Object o)
Returns true if this deque contains the specified element. More formally, returns true if and only if this deque contains at least one element e such that o.equals(e).
contains in interface Collection<E>
contains in interface Deque<E>
contains in class AbstractCollection<E>
o - object to be checked for containment in this dequetrue if this deque contains the specified elementpublic boolean remove(Object o)
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 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(Object).
remove in interface Collection<E>
remove in interface Deque<E>
remove in class AbstractCollection<E>
o - element to be removed from this deque, if presenttrue if this deque contained the specified elementpublic void clear()
Removes all of the elements from this deque. The deque will be empty after this call returns.
clear in interface Collection<E>
clear in class AbstractCollection<E>
public Object[] 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.
toArray in interface Collection<E>
toArray in class AbstractCollection<E>
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 x is a deque known to contain only strings. The following code can be used to dump the deque into a newly allocated array of String:
String[] y = x.toArray(new String[0]);Note that
toArray(new Object[0]) is identical in function to toArray().toArray in interface Collection<E>
toArray in class AbstractCollection<E>
T - the runtime type of the array to contain the collectiona - 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 purposeArrayStoreException - 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 nullpublic ArrayDeque<E> clone()
Returns a copy of this deque.
public Spliterator<E> spliterator()
Creates a late-binding and fail-fast Spliterator over the elements in this deque.
The Spliterator reports Spliterator.SIZED, Spliterator.SUBSIZED, Spliterator.ORDERED, and Spliterator.NONNULL. Overriding implementations should document the reporting of additional characteristic values.
spliterator in interface Iterable<E>
spliterator in interface Collection<E>
Spliterator over the elements in this deque
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