java.lang.Objectjava.util.AbstractCollection<E>
java.util.AbstractQueue<E>
public abstract class AbstractQueue<E>
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(E) 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
Java Collections Framework
.
Constructor Summary | |
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protected |
AbstractQueue
() Constructor for use by subclasses. |
Method Summary | |
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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. |
Methods inherited from class java.util. AbstractCollection |
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contains , containsAll , isEmpty , iterator , remove , removeAll , retainAll , size , toArray , toArray , toString |
Methods inherited from class java.lang. Object |
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clone , equals , finalize , getClass , hashCode , notify , notifyAll , wait , wait , wait |
Methods inherited from interface java.util. Queue |
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offer , peek , poll |
Methods inherited from interface java.util. Collection |
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contains , containsAll , equals , hashCode , isEmpty , iterator , remove , removeAll , retainAll , size , toArray , toArray |
Constructor Detail |
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protected AbstractQueue()
Method Detail |
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public boolean add(E e)
This implementation returns true if offer succeeds, else throws an IllegalStateException .
public E remove()
This implementation returns the result of poll unless the queue is empty.
public E element()
This implementation returns the result of peek unless the queue is empty.
public void clear()
This implementation repeatedly invokes poll until it returns null .
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.