java.util
Class AbstractQueue<E>
- Collection<E>, Iterable<E>, 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(E)
which does not permit
insertion of
null elements, along with methods
Queue.peek()
,
Queue.poll()
,
Collection.size()
, and a
Collection.iterator()
supporting
Iterator.remove()
. Typically, additional methods will be overridden
as well. If these requirements cannot be met, consider instead
subclassing
AbstractCollection
.
This class is a member of the
../../../technotes/guides/collections/index.html">
Java Collections Framework.
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(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.
|
T[] toArray , add , addAll , clear , contains , containsAll , isEmpty , iterator , remove , removeAll , retainAll , size , toArray , toString |
clone , equals , extends Object> getClass , finalize , hashCode , notify , notifyAll , toString , wait , wait , wait |
AbstractQueue
protected AbstractQueue()
Constructor for use by subclasses.
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.
- add in interface Queue<E>
- add in interface Collection<E>
- add in interface AbstractCollection<E>
addAll
public boolean addAll(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.
- addAll in interface Collection<E>
- addAll in interface AbstractCollection<E>
c
- collection containing elements to be added to this queue
- true if this queue changed as a result of the call
ClassCastException
- if the class of an element of the specified
collection prevents it from being added to this queueNullPointerException
- if the specified collection contains a
null element and this queue does not permit null elements,
or if the specified collection is nullIllegalArgumentException
- 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 queueIllegalStateException
- 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.
- clear in interface Collection<E>
- clear in interface AbstractCollection<E>
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.
- element in interface Queue<E>
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.
- remove in interface Queue<E>