AbstractQueue (Java Platform SE 8 ) (original) (raw)

• java.lang.Object

• • java.util.AbstractCollection
  • • java.util.AbstractQueue

• Type Parameters:
  E - the type of elements held in this collection
  All Implemented Interfaces:
  Iterable, Collection, Queue
  Direct Known Subclasses:
  ArrayBlockingQueue, ConcurrentLinkedQueue, DelayQueue, LinkedBlockingDeque, LinkedBlockingQueue, LinkedTransferQueue, PriorityBlockingQueue, PriorityQueue, SynchronousQueue

public abstract class AbstractQueue
extends AbstractCollection
implements Queue
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, andelement 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(), andCollection.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.
Since:
1.5

• • Constructor Summary

  Constructors

  Modifier	Constructor	Description
  protected	AbstractQueue()	Constructor for use by subclasses.

  • Method Summary

  All Methods Instance Methods Concrete Methods

  Modifier and Type	Method	Description
  boolean	add(E e)	Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returningtrue 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](../../java/util/AbstractCollection.html "class in java.util")  
     `[contains](../../java/util/AbstractCollection.html#contains-java.lang.Object-), [containsAll](../../java/util/AbstractCollection.html#containsAll-java.util.Collection-), [isEmpty](../../java/util/AbstractCollection.html#isEmpty--), [iterator](../../java/util/AbstractCollection.html#iterator--), [remove](../../java/util/AbstractCollection.html#remove-java.lang.Object-), [removeAll](../../java/util/AbstractCollection.html#removeAll-java.util.Collection-), [retainAll](../../java/util/AbstractCollection.html#retainAll-java.util.Collection-), [size](../../java/util/AbstractCollection.html#size--), [toArray](../../java/util/AbstractCollection.html#toArray--), [toArray](../../java/util/AbstractCollection.html#toArray-T:A-), [toString](../../java/util/AbstractCollection.html#toString--)`  
     * ### Methods inherited from class java.lang.[Object](../../java/lang/Object.html "class in java.lang")  
     `[clone](../../java/lang/Object.html#clone--), [equals](../../java/lang/Object.html#equals-java.lang.Object-), [finalize](../../java/lang/Object.html#finalize--), [getClass](../../java/lang/Object.html#getClass--), [hashCode](../../java/lang/Object.html#hashCode--), [notify](../../java/lang/Object.html#notify--), [notifyAll](../../java/lang/Object.html#notifyAll--), [wait](../../java/lang/Object.html#wait--), [wait](../../java/lang/Object.html#wait-long-), [wait](../../java/lang/Object.html#wait-long-int-)`  
     * ### Methods inherited from interface java.util.[Queue](../../java/util/Queue.html "interface in java.util")  
     `[offer](../../java/util/Queue.html#offer-E-), [peek](../../java/util/Queue.html#peek--), [poll](../../java/util/Queue.html#poll--)`  
     * ### Methods inherited from interface java.util.[Collection](../../java/util/Collection.html "interface in java.util")  
     `[contains](../../java/util/Collection.html#contains-java.lang.Object-), [containsAll](../../java/util/Collection.html#containsAll-java.util.Collection-), [equals](../../java/util/Collection.html#equals-java.lang.Object-), [hashCode](../../java/util/Collection.html#hashCode--), [isEmpty](../../java/util/Collection.html#isEmpty--), [iterator](../../java/util/Collection.html#iterator--), [parallelStream](../../java/util/Collection.html#parallelStream--), [remove](../../java/util/Collection.html#remove-java.lang.Object-), [removeAll](../../java/util/Collection.html#removeAll-java.util.Collection-), [removeIf](../../java/util/Collection.html#removeIf-java.util.function.Predicate-), [retainAll](../../java/util/Collection.html#retainAll-java.util.Collection-), [size](../../java/util/Collection.html#size--), [spliterator](../../java/util/Collection.html#spliterator--), [stream](../../java/util/Collection.html#stream--), [toArray](../../java/util/Collection.html#toArray--), [toArray](../../java/util/Collection.html#toArray-T:A-)`  
     * ### Methods inherited from interface java.lang.[Iterable](../../java/lang/Iterable.html "interface in java.lang")  
     `[forEach](../../java/lang/Iterable.html#forEach-java.util.function.Consumer-)`

• • Constructor Detail

     * #### AbstractQueue  
     protected AbstractQueue()  
     Constructor for use by subclasses.  

  • Method Detail

    * #### add  
    public boolean add([E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue") 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.  
    Specified by:  
    `[add](../../java/util/Collection.html#add-E-)` in interface `[Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>`  
    Specified by:  
    `[add](../../java/util/Queue.html#add-E-)` in interface `[Queue](../../java/util/Queue.html "interface in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>`  
    Overrides:  
    `[add](../../java/util/AbstractCollection.html#add-E-)` in class `[AbstractCollection](../../java/util/AbstractCollection.html "class in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>`  
    Parameters:  
    `e` \- the element to add  
    Returns:  
    true (as specified by [Collection.add(E)](../../java/util/Collection.html#add-E-))  
    Throws:  
    `[IllegalStateException](../../java/lang/IllegalStateException.html "class in java.lang")` \- if the element cannot be added at this time due to capacity restrictions  
    `[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the class of the specified element prevents it from being added to this queue  
    `[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if the specified element is null and this queue does not permit null elements  
    `[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if some property of this element prevents it from being added to this queue  
    * #### remove  
    public [E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue") remove()  
    Retrieves and removes the head of this queue. This method differs from [poll](../../java/util/Queue.html#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.  
    Specified by:  
    `[remove](../../java/util/Queue.html#remove--)` in interface `[Queue](../../java/util/Queue.html "interface in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>`  
    Returns:  
    the head of this queue  
    Throws:  
    `[NoSuchElementException](../../java/util/NoSuchElementException.html "class in java.util")` \- if this queue is empty  
    * #### element  
    public [E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue") element()  
    Retrieves, but does not remove, the head of this queue. This method differs from [peek](../../java/util/Queue.html#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.  
    Specified by:  
    `[element](../../java/util/Queue.html#element--)` in interface `[Queue](../../java/util/Queue.html "interface in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>`  
    Returns:  
    the head of this queue  
    Throws:  
    `[NoSuchElementException](../../java/util/NoSuchElementException.html "class in java.util")` \- if this queue is empty  
    * #### clear  
    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](../../java/util/Queue.html#poll--) until it returns null.  
    Specified by:  
    `[clear](../../java/util/Collection.html#clear--)` in interface `[Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>`  
    Overrides:  
    `[clear](../../java/util/AbstractCollection.html#clear--)` in class `[AbstractCollection](../../java/util/AbstractCollection.html "class in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>`  
    * #### addAll  
    public boolean addAll([Collection](../../java/util/Collection.html "interface in java.util")<? extends [E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")> 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, anull element) may result in only some of the elements having been successfully added when the associated exception is thrown.  
    Specified by:  
    `[addAll](../../java/util/Collection.html#addAll-java.util.Collection-)` in interface `[Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>`  
    Overrides:  
    `[addAll](../../java/util/AbstractCollection.html#addAll-java.util.Collection-)` in class `[AbstractCollection](../../java/util/AbstractCollection.html "class in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>`  
    Parameters:  
    `c` \- collection containing elements to be added to this queue  
    Returns:  
    true if this queue changed as a result of the call  
    Throws:  
    `[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the class of an element of the specified collection prevents it from being added to this queue  
    `[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if the specified collection contains a null element and this queue does not permit null elements, or if the specified collection is null  
    `[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- 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](../../java/lang/IllegalStateException.html "class in java.lang")` \- if not all the elements can be added at this time due to insertion restrictions  
    See Also:  
    [add(Object)](../../java/util/AbstractQueue.html#add-E-)

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