E- the type of elements held in this collection
public abstract class AbstractQueue<E> extends AbstractCollection<E> implements Queue<E>
Queueoperations. The implementations in this class are appropriate when the base implementation does not allow null elements. Methods
elementare based on
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
Collection.iterator(). Typically, additional methods will be overridden as well.
If these requirements cannot be met, consider instead subclassing
This class is a member of the Java Collections Framework.
|Modifier||Constructor and Description|
Constructor for use by subclasses.
|Modifier and Type||Method and Description|
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.
Adds all of the elements in the specified collection to this queue.
Removes all of the elements from this queue.
Retrieves, but does not remove, the head of this queue.
Retrieves and removes the head of this queue.
contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray, toString
clone, equals, getClass, hashCode, notify, notifyAll, wait, wait, wait
public boolean add(E e)
This implementation returns true if offer succeeds, else throws an IllegalStateException.
e- the element to add
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 addAll(Collection<? extends E> c)
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
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
public void clear()
This implementation repeatedly invokes
poll until it returns null.
public E element()
peekonly in that it throws an exception if this queue is empty.
This implementation returns the result of peek unless the queue is empty.
public E remove()
pollonly in that it throws an exception if this queue is empty.
This implementation returns the result of poll unless the queue is empty.