public abstract class AbstractQueue<E>
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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.

extends AbstractCollection<E> implements Queue<E>

<E>    the type of elements held in this collection

Since:  1.5