java.util.AbstractQueue<E>

public abstract class java.util

AbstractQueue<E>

Java SE 6

Extends: AbstractCollection

Implements: Queue

Extended by: ArrayBlockingQueue, ConcurrentLinkedQueue, DelayQueue, LinkedBlockingDeque, LinkedBlockingQueue, PriorityBlockingQueue, PriorityQueue, SynchronousQueue

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 a Collection#iterator supporting Iterator#remove. 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

E the type of elements held in this collection

Constructors

protected

AbstractQueue()
Constructor for use by subclasses.

Methods

public boolean

add(Object e) Details

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.

e the element to add

return true (as specified by Collection#add)

Throws IllegalStateException: if the element cannot be added at this time due to capacity restrictions

Throws ClassCastException: if the class of the specified element prevents it from being added to this queue

Throws NullPointerException: if the specified element is null and this queue does not permit null elements

Throws IllegalArgumentException: if some property of this element prevents it from being added to this queue

public boolean

addAll(Collection c) Details

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.

c collection containing elements to be added to this queue

return 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

Throws NullPointerException: if the specified collection contains a null element and this queue does not permit null elements, or if the specified collection is null

Throws 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

Throws IllegalStateException: if not all the elements can be added at this time due to insertion restrictions

See also add(Object)

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.

public Object

element() Details

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.

return the head of this queue

Throws NoSuchElementException: if this queue is empty

public Object

remove() Details

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.

return the head of this queue

Throws NoSuchElementException: if this queue is empty

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Java SE 6

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