Class AbstractQueue<E>
- java.lang.Object
-
- java.util.AbstractCollection<E>
-
- java.util.AbstractQueue<E>
- Type Parameters:
-
E
- the type of elements held in this queue
- All Implemented Interfaces:
-
Iterable<E>
,Collection<E>
,Queue<E>
- Direct Known Subclasses:
-
ArrayBlockingQueue
,ConcurrentLinkedQueue
,DelayQueue
,LinkedBlockingDeque
,LinkedBlockingQueue
,LinkedTransferQueue
,PriorityBlockingQueue
,PriorityQueue
,SynchronousQueue
public abstract class AbstractQueue<E> 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(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.
- Since:
- 1.5
Constructor Summary
Modifier | Constructor | Description |
---|---|---|
protected | AbstractQueue() | Constructor for use by subclasses. |
Method Summary
Modifier and Type | Method | 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 |
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. |
Methods declared in class java.util.AbstractCollection
contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, toArray, toArray, toString
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.Collection
contains, containsAll, equals, hashCode, isEmpty, iterator, parallelStream, remove, removeAll, removeIf, retainAll, size, spliterator, stream, toArray, toArray, toArray
Methods declared in interface java.lang.Iterable
forEach
Methods declared in interface java.util.Queue
offer, peek, poll
Constructor Detail
AbstractQueue
protected AbstractQueue()
Constructor for use by subclasses.
Method Detail
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
.
- Specified by:
-
add
in interfaceCollection<E>
- Specified by:
-
add
in interfaceQueue<E>
- Overrides:
-
add
in classAbstractCollection<E>
- Parameters:
-
e
- the element to add - Returns:
-
true
(as specified byCollection.add(E)
) - Throws:
-
IllegalStateException
- if the element cannot be added at this time due to capacity restrictions -
ClassCastException
- if the class of the specified element prevents it from being added to this queue -
NullPointerException
- if the specified element is null and this queue does not permit null elements -
IllegalArgumentException
- if some property of this element prevents it from being added to 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.
- Specified by:
-
remove
in interfaceQueue<E>
- Returns:
- the head of this queue
- Throws:
-
NoSuchElementException
- if this queue is empty
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.
- Specified by:
-
element
in interfaceQueue<E>
- Returns:
- the head of this queue
- Throws:
-
NoSuchElementException
- if this queue is empty
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
.
- Specified by:
-
clear
in interfaceCollection<E>
- Overrides:
-
clear
in classAbstractCollection<E>
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.
- Specified by:
-
addAll
in interfaceCollection<E>
- Overrides:
-
addAll
in classAbstractCollection<E>
- Parameters:
-
c
- collection containing elements to be added to this queue - Returns:
-
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 - See Also:
add(Object)