AbstractQueue

public abstract class AbstractQueue
extends AbstractCollection<E> implements Queue<E>

java.lang.Object
   ↳ java.util.AbstractCollection<E>
     ↳ java.util.AbstractQueue<E>
ArrayBlockingQueue<E> A bounded blocking queue backed by an array. 
ConcurrentLinkedQueue<E> An unbounded thread-safe queue based on linked nodes. 
DelayQueue<E extends Delayed> An unbounded blocking queue of Delayed elements, in which an element generally becomes eligible for removal when its delay has expired. 
LinkedBlockingDeque<E> An optionally-bounded blocking deque based on linked nodes. 
LinkedBlockingQueue<E> An optionally-bounded blocking queue based on linked nodes. 
LinkedTransferQueue<E> An unbounded TransferQueue based on linked nodes. 
PriorityBlockingQueue<E> An unbounded blocking queue that uses the same ordering rules as class PriorityQueue and supplies blocking retrieval operations. 
PriorityQueue<E> An unbounded priority queue based on a priority heap. 
SynchronousQueue<E> A blocking queue in which each insert operation must wait for a corresponding remove operation by another thread, and vice versa. 


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.

Summary

Protected constructors

AbstractQueue()

Constructor for use by subclasses.

Public methods

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.

Inherited methods

boolean add(E e)

Ensures that this collection contains the specified element (optional operation).

boolean addAll(Collection<? extends E> c)

Adds all of the elements in the specified collection to this collection (optional operation).

void clear()

Removes all of the elements from this collection (optional operation).

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).

abstract int size()

Returns the number of 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.

Object[] toArray()

Returns an array containing all of the elements in this collection.

String toString()

Returns a string representation of this collection.

Object clone()

Creates and returns a copy of this object.

boolean equals(Object obj)

Indicates whether some other object is "equal to" this one.

void finalize()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

final Class<?> getClass()

Returns the runtime class of this Object.

int hashCode()

Returns a hash code value for the object.

final void notify()

Wakes up a single thread that is waiting on this object's monitor.

final void notifyAll()

Wakes up all threads that are waiting on this object's monitor.

String toString()

Returns a string representation of the object.

final void wait(long timeoutMillis, int nanos)

Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

final void wait(long timeoutMillis)

Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

final void wait()

Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

abstract boolean add(E e)

Ensures that this collection contains the specified element (optional operation).

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

Adds all of the elements in the specified collection to this collection (optional operation).

abstract void clear()

Removes all of the elements from this collection (optional operation).

abstract boolean contains(Object o)

Returns true if this collection contains the specified element.

abstract boolean containsAll(Collection<?> c)

Returns true if this collection contains all of the elements in the specified collection.

abstract boolean equals(Object o)

Compares the specified object with this collection for equality.

abstract int hashCode()

Returns the hash code value for this collection.

abstract boolean isEmpty()

Returns true if this collection contains no elements.

abstract Iterator<E> iterator()

Returns an iterator over the elements in this collection.

default Stream<E> parallelStream()

Returns a possibly parallel Stream with this collection as its source.

abstract boolean remove(Object o)

Removes a single instance of the specified element from this collection, if it is present (optional operation).

abstract boolean removeAll(Collection<?> c)

Removes all of this collection's elements that are also contained in the specified collection (optional operation).

default boolean removeIf(Predicate<? super E> filter)

Removes all of the elements of this collection that satisfy the given predicate.

abstract boolean retainAll(Collection<?> c)

Retains only the elements in this collection that are contained in the specified collection (optional operation).

abstract 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.

abstract <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.

abstract Object[] toArray()

Returns an array containing all of the elements in this collection.

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.

abstract 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.

abstract E element()

Retrieves, but does not remove, the head of this queue.

abstract boolean offer(E e)

Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions.

abstract E peek()

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.

abstract E poll()

Retrieves and removes the head of this queue, or returns null if this queue is empty.

abstract E remove()

Retrieves and removes the head of this queue.

default void forEach(Consumer<? super T> action)

Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.

abstract Iterator<E> iterator()

Returns an iterator over elements of type T.

default Spliterator<E> spliterator()

Creates a Spliterator over the elements described by this Iterable.

Protected constructors

AbstractQueue

Added in API level 1
protected AbstractQueue ()

Constructor for use by subclasses.

Public methods

add

Added in API level 1
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.

Parameters
e E: the element to add

Returns
boolean true (as specified by Collection.add)

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

addAll

Added in API level 1
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.

Parameters
c Collection: collection containing elements to be added to this queue

Returns
boolean 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:

clear

Added in API level 1
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

Added in API level 1
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.

Returns
E the head of this queue

Throws
NoSuchElementException if this queue is empty

remove

Added in API level 1
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.

Returns
E the head of this queue

Throws
NoSuchElementException if this queue is empty