public class ArrayDeque extends AbstractCollection implements Deque, java.lang.Cloneable, java.io.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 an initial capacity
sufficient to hold 16 elements.
|
ArrayDeque(java.util.Collection 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(java.lang.Object e)
Inserts the specified element at the end of this deque.
|
void |
addFirst(java.lang.Object e)
Inserts the specified element at the front of this deque.
|
void |
addLast(java.lang.Object e)
Inserts the specified element at the end of this deque.
|
void |
clear()
Removes all of the elements from this deque.
|
java.lang.Object |
clone()
Returns a copy of this deque.
|
boolean |
contains(java.lang.Object o)
Returns true if this deque contains the specified element.
|
java.util.Iterator |
descendingIterator()
Returns an iterator over the elements in this deque in reverse
sequential order.
|
java.lang.Object |
element()
Retrieves, but does not remove, the head of the queue represented by
this deque.
|
java.lang.Object |
getFirst()
Retrieves, but does not remove, the first element of this deque.
|
java.lang.Object |
getLast()
Retrieves, but does not remove, the last element of this deque.
|
boolean |
isEmpty()
Returns true if this deque contains no elements.
|
java.util.Iterator |
iterator()
Returns an iterator over the elements in this deque.
|
boolean |
offer(java.lang.Object e)
Inserts the specified element at the end of this deque.
|
boolean |
offerFirst(java.lang.Object e)
Inserts the specified element at the front of this deque.
|
boolean |
offerLast(java.lang.Object e)
Inserts the specified element at the end of this deque.
|
java.lang.Object |
peek()
Retrieves, but does not remove, the head of the queue represented by
this deque, or returns null if this deque is empty.
|
java.lang.Object |
peekFirst()
Retrieves, but does not remove, the first element of this deque,
or returns null if this deque is empty.
|
java.lang.Object |
peekLast()
Retrieves, but does not remove, the last 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 |
pollFirst()
Retrieves and removes the first element of this deque,
or returns null if this deque is empty.
|
java.lang.Object |
pollLast()
Retrieves and removes the last element of this deque,
or returns null if this deque is empty.
|
java.lang.Object |
pop()
Pops an element from the stack represented by this deque.
|
void |
push(java.lang.Object e)
Pushes an element onto the stack represented by this deque.
|
java.lang.Object |
remove()
Retrieves and removes the head of the queue represented by this deque.
|
boolean |
remove(java.lang.Object o)
Removes a single instance of the specified element from this deque.
|
java.lang.Object |
removeFirst()
Retrieves and removes the first element of this deque.
|
boolean |
removeFirstOccurrence(java.lang.Object o)
Removes the first occurrence of the specified element in this
deque (when traversing the deque from head to tail).
|
java.lang.Object |
removeLast()
Retrieves and removes the last element of this deque.
|
boolean |
removeLastOccurrence(java.lang.Object o)
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.
|
java.lang.Object[] |
toArray()
Returns an array containing all of the elements in this deque
in proper sequence (from first to last element).
|
java.lang.Object[] |
toArray(java.lang.Object[] 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.
|
addAll, containsAll, removeAll, retainAll, toString
public ArrayDeque()
public ArrayDeque(int numElements)
numElements
- lower bound on initial capacity of the dequepublic ArrayDeque(java.util.Collection c)
c
- the collection whose elements are to be placed into the dequejava.lang.NullPointerException
- if the specified collection is nullpublic void addFirst(java.lang.Object e)
public void addLast(java.lang.Object e)
This method is equivalent to add(java.lang.Object)
.
public boolean offerFirst(java.lang.Object e)
offerFirst
in interface Deque
e
- the element to addDeque.offerFirst(java.lang.Object)
)java.lang.NullPointerException
- if the specified element is nullpublic boolean offerLast(java.lang.Object e)
offerLast
in interface Deque
e
- the element to addDeque.offerLast(java.lang.Object)
)java.lang.NullPointerException
- if the specified element is nullpublic java.lang.Object removeFirst()
Deque
pollFirst
only in that it throws an
exception if this deque is empty.removeFirst
in interface Deque
java.util.NoSuchElementException
public java.lang.Object removeLast()
Deque
pollLast
only in that it throws an
exception if this deque is empty.removeLast
in interface Deque
java.util.NoSuchElementException
public java.lang.Object pollFirst()
Deque
public java.lang.Object pollLast()
Deque
public java.lang.Object getFirst()
Deque
peekFirst
only in that it
throws an exception if this deque is empty.public java.lang.Object getLast()
Deque
peekLast
only in that it
throws an exception if this deque is empty.public java.lang.Object peekFirst()
Deque
public java.lang.Object peekLast()
Deque
public boolean removeFirstOccurrence(java.lang.Object o)
removeFirstOccurrence
in interface Deque
o
- element to be removed from this deque, if presentpublic boolean removeLastOccurrence(java.lang.Object o)
removeLastOccurrence
in interface Deque
o
- element to be removed from this deque, if presentpublic boolean add(java.lang.Object e)
This method is equivalent to addLast(java.lang.Object)
.
add
in interface Deque
add
in interface Queue
add
in interface java.util.Collection
add
in class java.util.AbstractCollection
e
- the element to addCollection.add(java.lang.Object)
)java.lang.NullPointerException
- if the specified element is nullpublic boolean offer(java.lang.Object e)
This method is equivalent to offerLast(java.lang.Object)
.
offer
in interface Deque
offer
in interface Queue
e
- the element to addQueue.offer(java.lang.Object)
)java.lang.NullPointerException
- if the specified element is nullpublic java.lang.Object remove()
poll
only in that it throws an
exception if this deque is empty.
This method is equivalent to removeFirst()
.
public java.lang.Object poll()
This method is equivalent to pollFirst()
.
public java.lang.Object element()
peek
only in
that it throws an exception if this deque is empty.
This method is equivalent to getFirst()
.
public java.lang.Object peek()
This method is equivalent to peekFirst()
.
public void push(java.lang.Object e)
This method is equivalent to addFirst(java.lang.Object)
.
public java.lang.Object pop()
This method is equivalent to removeFirst()
.
public int size()
public boolean isEmpty()
isEmpty
in interface java.util.Collection
isEmpty
in class java.util.AbstractCollection
public java.util.Iterator iterator()
public java.util.Iterator descendingIterator()
Deque
descendingIterator
in interface Deque
public boolean contains(java.lang.Object o)
public boolean remove(java.lang.Object o)
This method is equivalent to removeFirstOccurrence(java.lang.Object)
.
public void clear()
clear
in interface java.util.Collection
clear
in class java.util.AbstractCollection
public java.lang.Object[] toArray()
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 java.util.Collection
toArray
in class AbstractCollection
public java.lang.Object[] toArray(java.lang.Object[] a)
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 java.util.Collection
toArray
in class AbstractCollection
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 purposejava.lang.ArrayStoreException
- if the runtime type of the specified array
is not a supertype of the runtime type of every element in
this dequejava.lang.NullPointerException
- if the specified array is nullpublic java.lang.Object clone()
clone
in class java.lang.Object