OpenJDK 1.22 · java.util.AbstractQueue · APIdia, the JavaDoc alternative

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 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.

Access	Constructor and Description
protected	AbstractQueue() Constructor for use by subclasses.

Method Summary

Modifier and Type	Method and Description
public boolean	Returns: `true` (as specified by `Collection#add`) add(E the element to add e) Overrides java.util.AbstractCollection.add. Implements java.util.Queue.add, java.util.Collection.add. 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.
public boolean	Returns: `true` if this queue changed as a result of the call addAll(Collection<? extends E> collection containing elements to be added to this queue c) Overrides java.util.AbstractCollection.addAll. Implements java.util.Collection.addAll. Adds all of the elements in the specified collection to this queue.
public void	clear() Overrides java.util.AbstractCollection.clear. Implements java.util.Collection.clear. Removes all of the elements from this queue.
public E	Returns: the head of this queue element() Implements java.util.Queue.element. Retrieves, but does not remove, the head of this queue.
public E	Returns: the head of this queue remove() Implements java.util.Queue.remove. Retrieves and removes the head of this queue.

Inherited from java.util.AbstractCollection:: contains containsAll isEmpty iterator remove removeAll retainAll size toArray toArray toString

Constructor Detail

AbstractQueue	back to summary
protected AbstractQueue() Constructor for use by subclasses.

Method Detail

add back to summary

add	back to summary
public boolean add(E e) Overrides java.util.AbstractCollection.add. Implements java.util.Queue.add, java.util.Collection.add. 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`. Parameters e:E the element to add Returns:boolean `true` (as specified by `Collection#add`) Exceptions 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

public boolean add(E e)

Overrides java.util.AbstractCollection.add.

Implements java.util.Queue.add, java.util.Collection.add.

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.

Parameters

e:E: the element to add

Returns:boolean

true (as specified by Collection#add)

Exceptions

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

addAll back to summary

addAll	back to summary
public boolean addAll(Collection<? extends E> c) Overrides java.util.AbstractCollection.addAll. Implements java.util.Collection.addAll. 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. Parameters c:Collection<? extends E> collection containing elements to be added to this queue Returns:boolean `true` if this queue changed as a result of the call Exceptions 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)`

public boolean addAll(Collection<? extends E> c)

Overrides java.util.AbstractCollection.addAll.

Implements java.util.Collection.addAll.

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.

Parameters

c:Collection<? extends E>: collection containing elements to be added to this queue

Returns:boolean

true if this queue changed as a result of the call

Exceptions

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)

clear back to summary

clear	back to summary
public void clear() Overrides java.util.AbstractCollection.clear. Implements java.util.Collection.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`.

public void clear()

Overrides java.util.AbstractCollection.clear.

Implements java.util.Collection.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 back to summary

element	back to summary
public E element() Implements java.util.Queue.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. Returns:E the head of this queue Exceptions NoSuchElementException: if this queue is empty

public E element()

Implements java.util.Queue.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.

Returns:E

the head of this queue

Exceptions

NoSuchElementException:: if this queue is empty

remove back to summary

remove	back to summary
public E remove() Implements java.util.Queue.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. Returns:E the head of this queue Exceptions NoSuchElementException: if this queue is empty

public E remove()

Implements java.util.Queue.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.

Returns:E

the head of this queue

Exceptions

NoSuchElementException:: if this queue is empty

public abstract Class AbstractQueue<E>

Constructor Summary

Method Summary

Constructor Detail

Method Detail