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

Constructors

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 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 AbstractCollection

contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, toArray, toArray, toString

Modifier and Type	Method	Description
boolean	contains(Object o)	Returns true if this collection contains the specified element.
boolean	containsAll(Collection<?> c)	Returns true if this collection contains all of the elements in the specified collection.
boolean	isEmpty()	Returns true if this collection contains no elements.
abstract Iterator<E>	iterator()	Returns an iterator over the elements contained in this collection.
boolean	remove(Object o)	Removes a single instance of the specified element from this collection, if it is present (optional operation).
boolean	removeAll(Collection<?> c)	Removes all of this collection's elements that are also contained in the specified collection (optional operation).
boolean	retainAll(Collection<?> c)	Retains only the elements in this collection that are contained in the specified collection (optional operation).
Object[]	toArray()	Returns an array containing all of the elements in this collection.
<T> T[]	toArray(T[] a)	Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
String	toString()	Returns a string representation of this collection.

Methods declared in class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Modifier and Type	Method	Description
protected Object	clone()	Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
boolean	equals(Object o)	Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.
protected void	finalize()	Deprecated, for removal: This API element is subject to removal in a future version. May cause performance issues, deadlocks and hangs.
final Class<? extends Object>	getClass()	Answers the unique instance of java.lang.Class which represents the class of the receiver.
int	hashCode()	Answers an integer hash code for the receiver.
final void	notify()	Causes one thread which is waiting on the receiver to be made ready to run.
final void	notifyAll()	Causes all threads which are waiting on the receiver to be made ready to run.
final void	wait()	Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).
final void	wait(long time)	Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.
final void	wait(long time, int frac)	Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

Methods declared in interface Collection

equals, hashCode, parallelStream, removeIf, size, spliterator, stream, toArray

Modifier and Type	Method	Description
boolean	equals(Object o)	Compares the specified object with this collection for equality.
int	hashCode()	Returns the hash code value for this collection.
default Stream<E>	parallelStream()	Returns a possibly parallel Stream with this collection as its source.
default boolean	removeIf(Predicate<? super E> filter)	Removes all of the elements of this collection that satisfy the given predicate (optional operation).
int	size()	Returns the number of elements in this collection.
default Spliterator<E>	spliterator()	Creates a Spliterator over the elements in this collection.
default Stream<E>	stream()	Returns a sequential Stream with this collection as its source.
default <T> T[]	toArray(IntFunction<T[]> generator)	Returns an array containing all of the elements in this collection, using the provided generator function to allocate the returned array.

Methods declared in interface Iterable

forEach

Modifier and Type	Method	Description
default void	forEach(Consumer<? super E> action)	Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.

Methods declared in interface Queue

offer, peek, poll

Modifier and Type	Method	Description
boolean	offer(E e)	Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions.
E	peek()	Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
E	poll()	Retrieves and removes the head of this queue, or returns null if this queue is empty.

Constructor Details

AbstractQueue

protected AbstractQueue()

Constructor for use by subclasses.

Method Details

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)