edu.emory.mathcs.backport.java.util
Class AbstractQueue
java.util.AbstractCollection
- Collection, Queue
public abstract class AbstractQueue
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(Object)
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
../../../../../../../guide/collections/index.html">
Java Collections Framework.
boolean | add(Object 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 c) - Adds all of the elements in the specified collection to this
queue.
|
void | clear() - Removes all of the elements from this queue.
|
Object | element() - Retrieves, but does not remove, the head of this queue.
|
Object | remove() - Retrieves and removes the head of this queue.
|
AbstractQueue
protected AbstractQueue()
Constructor for use by subclasses.
add
public boolean add(Object 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
- true (as specified by
Collection.add
)
addAll
public boolean addAll(Collection 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.
c
- collection containing elements to be added to this queue
- true if this queue changed as a result of the call
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 Object 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
remove
public Object 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