AbstractQueue
public
abstract
class
AbstractQueue
extends AbstractCollection<E>
implements
Queue<E>
This class provides skeletal implementations of some Queue
operations. The implementations in this class are appropriate when
the base implementation does not allow null
elements. Methods add
, remove
, and
element
are based on offer
, poll
, and peek
, respectively, but throw
exceptions instead of indicating failure via false
or
null
returns.
A Queue
implementation that extends this class must
minimally define a method Queue.offer
which does not permit
insertion of null
elements, along with methods Queue.peek()
, Queue.poll
, Collection.size
, and
Collection.iterator
. Typically, additional methods will be
overridden as well. If these requirements cannot be met, consider
instead subclassing AbstractCollection
.
Summary
Protected constructors |
AbstractQueue()
Constructor for use by subclasses.
|
Public methods |
boolean
|
add(E e)
Inserts the specified element into this queue if it is possible to do so
immediately without violating capacity restrictions, returning
true upon success and throwing an IllegalStateException
if no space is currently available.
|
boolean
|
addAll(Collection<? extends E> c)
Adds all of the elements in the specified collection to this
queue.
|
void
|
clear()
Removes all of the elements from this queue.
|
E
|
element()
Retrieves, but does not remove, the head of this queue.
|
E
|
remove()
Retrieves and removes the head of this queue.
|
Inherited methods |
From class
java.util.AbstractCollection
boolean
|
add(E e)
Ensures that this collection contains the specified element (optional
operation).
|
boolean
|
addAll(Collection<? extends E> c)
Adds all of the elements in the specified collection to this collection
(optional operation).
|
void
|
clear()
Removes all of the elements from this collection (optional operation).
|
boolean
|
contains(Object o)
Returns true if this collection contains the specified element.
|
boolean
|
containsAll(Collection<?> c)
Returns true if this collection contains all of the elements
in the specified collection.
|
boolean
|
isEmpty()
Returns true if this collection contains no elements.
|
abstract
Iterator<E>
|
iterator()
Returns an iterator over the elements contained in this collection.
|
boolean
|
remove(Object o)
Removes a single instance of the specified element from this
collection, if it is present (optional operation).
|
boolean
|
removeAll(Collection<?> c)
Removes all of this collection's elements that are also contained in the
specified collection (optional operation).
|
boolean
|
retainAll(Collection<?> c)
Retains only the elements in this collection that are contained in the
specified collection (optional operation).
|
abstract
int
|
size()
Returns the number of elements in this collection.
|
<T>
T[]
|
toArray(T[] a)
Returns an array containing all of the elements in this collection;
the runtime type of the returned array is that of the specified array.
|
Object[]
|
toArray()
Returns an array containing all of the elements in this collection.
|
String
|
toString()
Returns a string representation of this collection.
|
|
From class
java.lang.Object
Object
|
clone()
Creates and returns a copy of this object.
|
boolean
|
equals(Object obj)
Indicates whether some other object is "equal to" this one.
|
void
|
finalize()
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
|
final
Class<?>
|
getClass()
Returns the runtime class of this Object .
|
int
|
hashCode()
Returns a hash code value for the object.
|
final
void
|
notify()
Wakes up a single thread that is waiting on this object's
monitor.
|
final
void
|
notifyAll()
Wakes up all threads that are waiting on this object's monitor.
|
String
|
toString()
Returns a string representation of the object.
|
final
void
|
wait(long timeoutMillis, int nanos)
Causes the current thread to wait until it is awakened, typically
by being notified or interrupted, or until a
certain amount of real time has elapsed.
|
final
void
|
wait(long timeoutMillis)
Causes the current thread to wait until it is awakened, typically
by being notified or interrupted, or until a
certain amount of real time has elapsed.
|
final
void
|
wait()
Causes the current thread to wait until it is awakened, typically
by being notified or interrupted.
|
|
From interface
java.util.Collection
abstract
boolean
|
add(E e)
Ensures that this collection contains the specified element (optional
operation).
|
abstract
boolean
|
addAll(Collection<? extends E> c)
Adds all of the elements in the specified collection to this collection
(optional operation).
|
abstract
void
|
clear()
Removes all of the elements from this collection (optional operation).
|
abstract
boolean
|
contains(Object o)
Returns true if this collection contains the specified element.
|
abstract
boolean
|
containsAll(Collection<?> c)
Returns true if this collection contains all of the elements
in the specified collection.
|
abstract
boolean
|
equals(Object o)
Compares the specified object with this collection for equality.
|
abstract
int
|
hashCode()
Returns the hash code value for this collection.
|
abstract
boolean
|
isEmpty()
Returns true if this collection contains no elements.
|
abstract
Iterator<E>
|
iterator()
Returns an iterator over the elements in this collection.
|
default
Stream<E>
|
parallelStream()
Returns a possibly parallel Stream with this collection as its
source.
|
abstract
boolean
|
remove(Object o)
Removes a single instance of the specified element from this
collection, if it is present (optional operation).
|
abstract
boolean
|
removeAll(Collection<?> c)
Removes all of this collection's elements that are also contained in the
specified collection (optional operation).
|
default
boolean
|
removeIf(Predicate<? super E> filter)
Removes all of the elements of this collection that satisfy the given
predicate.
|
abstract
boolean
|
retainAll(Collection<?> c)
Retains only the elements in this collection that are contained in the
specified collection (optional operation).
|
abstract
int
|
size()
Returns the number of elements in this collection.
|
default
Spliterator<E>
|
spliterator()
Creates a Spliterator over the elements in this collection.
|
default
Stream<E>
|
stream()
Returns a sequential Stream with this collection as its source.
|
abstract
<T>
T[]
|
toArray(T[] a)
Returns an array containing all of the elements in this collection;
the runtime type of the returned array is that of the specified array.
|
abstract
Object[]
|
toArray()
Returns an array containing all of the elements in this collection.
|
default
<T>
T[]
|
toArray(IntFunction<T[]> generator)
Returns an array containing all of the elements in this collection,
using the provided generator function to allocate the returned array.
|
|
From interface
java.util.Queue
abstract
boolean
|
add(E e)
Inserts the specified element into this queue if it is possible to do so
immediately without violating capacity restrictions, returning
true upon success and throwing an IllegalStateException
if no space is currently available.
|
abstract
E
|
element()
Retrieves, but does not remove, the head of this queue.
|
abstract
boolean
|
offer(E e)
Inserts the specified element into this queue if it is possible to do
so immediately without violating capacity restrictions.
|
abstract
E
|
peek()
Retrieves, but does not remove, the head of this queue,
or returns null if this queue is empty.
|
abstract
E
|
poll()
Retrieves and removes the head of this queue,
or returns null if this queue is empty.
|
abstract
E
|
remove()
Retrieves and removes the head of this queue.
|
|
From interface
java.lang.Iterable
default
void
|
forEach(Consumer<? super T> action)
Performs the given action for each element of the Iterable
until all elements have been processed or the action throws an
exception.
|
abstract
Iterator<E>
|
iterator()
Returns an iterator over elements of type T .
|
default
Spliterator<E>
|
spliterator()
Creates a Spliterator over the elements described by this
Iterable .
|
|
Protected constructors
AbstractQueue
protected AbstractQueue ()
Constructor for use by subclasses.
Public methods
add
public boolean add (E e)
Inserts the specified element into this queue if it is possible to do so
immediately without violating capacity restrictions, returning
true
upon success and throwing an IllegalStateException
if no space is currently available.
This implementation returns true
if offer
succeeds,
else throws an IllegalStateException
.
Parameters |
e |
E : the element to add |
addAll
public boolean addAll (Collection<? extends E> c)
Adds all of the elements in the specified collection to this
queue. Attempts to addAll of a queue to itself result in
IllegalArgumentException
. Further, the behavior of
this operation is undefined if the specified collection is
modified while the operation is in progress.
This implementation iterates over the specified collection,
and adds each element returned by the iterator to this
queue, in turn. A runtime exception encountered while
trying to add an element (including, in particular, a
null
element) may result in only some of the elements
having been successfully added when the associated exception is
thrown.
Parameters |
c |
Collection : collection containing elements to be added to this queue |
Returns |
boolean |
true if this queue changed as a result of the call |
Throws |
ClassCastException |
if the class of an element of the specified
collection prevents it from being added to this queue |
NullPointerException |
if the specified collection contains a
null element and this queue does not permit null elements,
or if the specified collection is null |
IllegalArgumentException |
if some property of an element of the
specified collection prevents it from being added to this
queue, or if the specified collection is this queue |
IllegalStateException |
if not all the elements can be added at
this time due to insertion restrictions |
clear
public void clear ()
Removes all of the elements from this queue.
The queue will be empty after this call returns.
This implementation repeatedly invokes poll
until it
returns null
.
element
public E element ()
Retrieves, but does not remove, the head of this queue. This method
differs from peek
only in that it throws an exception if
this queue is empty.
This implementation returns the result of peek
unless the queue is empty.
Returns |
E |
the head of this queue |
remove
public E remove ()
Retrieves and removes the head of this queue. This method differs
from poll
only in that it throws an exception if this
queue is empty.
This implementation returns the result of poll
unless the queue is empty.
Returns |
E |
the head of this queue |