Class 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

Constructors

Modifier Constructor Description
protected AbstractQueue()

Constructor for use by subclasses.

Methods

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 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.

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

Constructors

AbstractQueue

protected AbstractQueue()

Constructor for use by subclasses.

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.

Specified by:
add in interface Collection<E>
Specified by:
add in interface Queue<E>
Overrides:
add in class AbstractCollection<E>
Parameters:
e - the element to add
Returns:
true (as specified by Collection.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 interface Queue<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 interface Queue<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 interface Collection<E>
Overrides:
clear in class AbstractCollection<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 interface Collection<E>
Overrides:
addAll in class AbstractCollection<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)

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https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/AbstractQueue.html