E
- the type of elements held in this collectionpublic abstract class AbstractQueue<E> extends AbstractCollection<E> implements Queue<E>
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
Collection.iterator()
. 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 Java Collections Framework.
Modifier | Constructor and Description |
---|---|
protected |
AbstractQueue()
Constructor for use by subclasses.
|
Modifier and Type | Method and Description |
---|---|
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.
|
contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray, toString
public boolean add(E e)
This implementation returns true if offer succeeds, else throws an IllegalStateException.
add
in interface Collection<E>
add
in interface Queue<E>
add
in class AbstractCollection<E>
e
- the element to addCollection.add(E)
)IllegalStateException
- if the element cannot be added at this
time due to capacity restrictionsClassCastException
- if the class of the specified element
prevents it from being added to this queueNullPointerException
- if the specified element is null and
this queue does not permit null elementsIllegalArgumentException
- if some property of this element
prevents it from being added to this queuepublic boolean addAll(Collection<? extends E> c)
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 class AbstractCollection<E>
c
- collection containing elements to be added to this queueClassCastException
- 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 restrictionsadd(Object)
public void clear()
This implementation repeatedly invokes poll
until it
returns null.
clear
in interface Collection<E>
clear
in class AbstractCollection<E>
public E element()
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>
NoSuchElementException
- if this queue is emptypublic E remove()
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>
NoSuchElementException
- if this queue is emptyCopyright (c) 2014, Oracle and/or its affiliates. All rights reserved. Use of this specification is subject to license terms.