E
- the type of elements held in this collectionpublic class ArrayQueue<E> extends AbstractCollection<E> implements Queue<E>, Cloneable, Serializable
Queue
interface. Array
queues 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
LinkedList
when used as a queue.
Most ArrayBackedQueue operations run in amortized constant time.
Exceptions include remove
, removeFirstOccurrence
, 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 queue 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.
Constructor and Description |
---|
ArrayQueue()
Constructs an empty array queue with an initial capacity
sufficient to hold 16 elements.
|
ArrayQueue(Collection<? extends E> c)
Constructs a queue containing the elements of the specified
collection, in the order they are returned by the collection's
iterator.
|
ArrayQueue(int numElements)
Constructs an empty array queue 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 at the end of this queue.
|
void |
clear()
Removes all of the elements from this queue.
|
ArrayQueue<E> |
clone()
Returns a copy of this queue.
|
boolean |
contains(Object o)
Returns true if this queue contains the specified element.
|
E |
element()
Retrieves, but does not remove, the head of the queue represented by
this queue.
|
boolean |
isEmpty()
Returns true if this queue contains no elements.
|
Iterator<E> |
iterator()
Returns an iterator over the elements in this queue.
|
boolean |
offer(E e)
Inserts the specified element at the end of this queue.
|
E |
peek()
Retrieves, but does not remove, the head of the queue represented by
this queue, or returns null if this queue is empty.
|
E |
poll()
Retrieves and removes the head of the queue represented by this queue
(in other words, the first element of this queue), or returns
null if this queue is empty.
|
E |
remove()
Retrieves and removes the head of the queue represented by this queue.
|
boolean |
remove(Object o)
Removes a single instance of the specified element from this queue.
|
int |
size()
Returns the number of elements in this queue.
|
Object[] |
toArray()
Returns an array containing all of the elements in this queue
in proper sequence (from first to last element).
|
<T> T[] |
toArray(T[] a)
Returns an array containing all of the elements in this queue 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
equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
addAll, containsAll, equals, hashCode, parallelStream, removeAll, removeIf, retainAll, spliterator, stream
public ArrayQueue()
public ArrayQueue(int numElements)
numElements
- lower bound on initial capacity of the queuepublic ArrayQueue(Collection<? extends E> c)
c
- the collection whose elements are to be placed into the queueNullPointerException
- if the specified collection is nullpublic boolean add(E e)
This method is equivalent to offer(E)
.
add
in interface Collection<E>
add
in interface Queue<E>
add
in class AbstractCollection<E>
e
- the element to addCollection.add(E)
)NullPointerException
- if the specified element is nullpublic boolean offer(E e)
offer
in interface Queue<E>
e
- the element to addQueue.offer(E)
)NullPointerException
- if the specified element is nullpublic E remove()
poll
only in that it throws an
exception if this queue is empty.remove
in interface Queue<E>
NoSuchElementException
public E poll()
public E element()
peek
only in
that it throws an exception if this queue is empty.element
in interface Queue<E>
NoSuchElementException
public E peek()
public 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 Iterator<E> iterator()
remove()
or popped (via successive calls to #pop
).iterator
in interface Iterable<E>
iterator
in interface Collection<E>
iterator
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 queuepublic boolean remove(Object o)
remove
in interface Collection<E>
remove
in class AbstractCollection<E>
o
- element to be removed from this queue, if presentpublic void clear()
clear
in interface Collection<E>
clear
in class AbstractCollection<E>
public Object[] toArray()
The returned array will be "safe" in that no references to it are maintained by this queue. (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)
If this queue fits in the specified array with room to spare (i.e., the array has more elements than this queue), the element in the array immediately following the end of the queue 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 queue known to contain only strings. The following code can be used to dump the queue 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>
a
- the array into which the elements of the queue 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 queueNullPointerException
- if the specified array is nullpublic ArrayQueue<E> clone()
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