E
- the type of elements held in this collectionpublic class ArrayDeque<E> extends AbstractCollection<E> implements Deque<E>, Cloneable, Serializable
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.
Constructor and Description |
---|
ArrayDeque()
Constructs an empty array deque with the an initial capacity
sufficient to hold 16 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.
|
ArrayDeque(int numElements)
Constructs an empty array deque with an initial capacity
sufficient to hold the specified number of elements.
|
Modifier and Type | Method and Description |
---|---|
boolean |
add(E e)
Inserts the specified element to the end of this deque.
|
void |
addFirst(E e)
Inserts the specified element to the front this deque.
|
void |
addLast(E e)
Inserts the specified element to the end this deque.
|
void |
clear()
Removes all of the elements from this deque.
|
ArrayDeque<E> |
clone()
Returns a copy of this deque.
|
boolean |
contains(Object o)
Returns true if this deque contains the specified
element.
|
E |
element()
Retrieves, but does not remove, the head of the queue represented by
this deque.
|
E |
getFirst()
Retrieves, but does not remove, the first element of this
deque.
|
E |
getLast()
Retrieves, but does not remove, the last element of this
deque.
|
boolean |
isEmpty()
Returns true if this collection contains no elements.
|
Iterator<E> |
iterator()
Returns an iterator over the elements in this deque.
|
boolean |
offer(E e)
Inserts the specified element to the end of this deque.
|
boolean |
offerFirst(E e)
Inserts the specified element to the front this deque.
|
boolean |
offerLast(E e)
Inserts the specified element to the end this deque.
|
E |
peek()
Retrieves, but does not remove, the head of the queue represented by
this deque, returning null if this deque is empty.
|
E |
peekFirst()
Retrieves, but does not remove, the first element of this deque,
returning null if this deque is empty.
|
E |
peekLast()
Retrieves, but does not remove, the last element of this deque,
returning null if this deque is empty.
|
E |
poll()
Retrieves and removes the head of the queue represented by
this deque, or null if this deque is empty.
|
E |
pollFirst()
Retrieves and removes the first element of this deque, or
null if this deque is empty.
|
E |
pollLast()
Retrieves and removes the last element of this deque, or
null if this deque is empty.
|
E |
pop()
Pops an element from the stack represented by this deque.
|
void |
push(E e)
Pushes an element onto the stack represented by this deque.
|
E |
remove()
Retrieves and removes the head of the queue represented by this deque.
|
boolean |
remove(Object e)
Removes a single instance of the specified element from this deque.
|
E |
removeFirst()
Retrieves and removes the first element of this deque.
|
boolean |
removeFirstOccurrence(Object e)
Removes the first occurrence of the specified element in this
deque (when traversing the deque from head to tail).
|
E |
removeLast()
Retrieves and removes the last element of this deque.
|
boolean |
removeLastOccurrence(Object e)
Removes the last occurrence of the specified element in this
deque (when traversing the deque from head to tail).
|
int |
size()
Returns the number of elements in this deque.
|
Object[] |
toArray()
Returns an array containing all of the elements in this list
in the correct order.
|
<T> T[] |
toArray(T[] a)
Returns an array containing all of the elements in this deque in the
correct order; the runtime type of the returned array is that of the
specified array.
|
addAll, containsAll, removeAll, retainAll, toString
equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
addAll, containsAll, equals, hashCode, removeAll, retainAll
public ArrayDeque()
public ArrayDeque(int numElements)
numElements
- lower bound on initial capacity of the dequepublic ArrayDeque(Collection<? extends E> c)
c
- the collection whose elements are to be placed into the dequeNullPointerException
- if the specified collection is nullpublic void addFirst(E e)
addFirst
in interface Deque<E>
e
- the element to insertNullPointerException
- if e is nullpublic void addLast(E e)
Collection.add(E)
and
push(E)
.addLast
in interface Deque<E>
e
- the element to insertNullPointerException
- if e is nullpublic E pollFirst()
public E pollLast()
public boolean offerFirst(E e)
offerFirst
in interface Deque<E>
e
- the element to insertDeque.offerFirst(E)
)NullPointerException
- if e is nullpublic boolean offerLast(E e)
offerLast
in interface Deque<E>
e
- the element to insertDeque.offerLast(E)
)NullPointerException
- if e is nullpublic E removeFirst()
removeFirst
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic E removeLast()
removeLast
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic E peekFirst()
public E peekLast()
public E getFirst()
getFirst
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic E getLast()
getLast
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic boolean removeFirstOccurrence(Object e)
removeFirstOccurrence
in interface Deque<E>
e
- element to be removed from this deque, if presentpublic boolean removeLastOccurrence(Object e)
removeLastOccurrence
in interface Deque<E>
e
- element to be removed from this deque, if presentpublic boolean offer(E e)
This method is equivalent to offerLast(E)
.
offer
in interface Queue<E>
offer
in interface Deque<E>
e
- the element to insertQueue.offer(E)
)NullPointerException
- if e is nullpublic boolean add(E e)
This method is equivalent to addLast(E)
.
add
in interface Collection<E>
add
in interface Queue<E>
add
in interface Deque<E>
add
in class AbstractCollection<E>
e
- the element to insertCollection.add(E)
)NullPointerException
- if e is nullpublic E poll()
This method is equivalent to pollFirst()
.
public E remove()
This method is equivalent to removeFirst()
.
public E peek()
This method is equivalent to peekFirst()
public E element()
This method is equivalent to getFirst()
public void push(E e)
This method is equivalent to addFirst(E)
.
push
in interface Deque<E>
e
- the element to pushNullPointerException
- if e is nullpublic E pop()
This method is equivalent to removeFirst()
.
pop
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic int size()
size
in interface Collection<E>
size
in class AbstractCollection<E>
public boolean isEmpty()
isEmpty
in interface Collection<E>
isEmpty
in class AbstractCollection<E>
public boolean contains(Object o)
contains
in interface Collection<E>
contains
in class AbstractCollection<E>
o
- object to be checked for containment in this dequepublic boolean remove(Object e)
removeFirstOccurrence(java.lang.Object)
.remove
in interface Collection<E>
remove
in class AbstractCollection<E>
e
- element to be removed from this deque, if presentpublic void clear()
clear
in interface Collection<E>
clear
in class AbstractCollection<E>
public Object[] toArray()
toArray
in interface Collection<E>
toArray
in class AbstractCollection<E>
public <T> T[] toArray(T[] a)
If the deque fits in the specified array with room to spare (i.e., the array has more elements than the deque), the element in the array immediately following the end of the collection is set to null.
toArray
in interface Collection<E>
toArray
in class AbstractCollection<E>
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 purposeArrayStoreException
- if the runtime type of a is not a supertype
of the runtime type of every element in this dequepublic ArrayDeque<E> clone()