AbstractQueue (Java 2 Platform SE 5.0) (original) (raw)

java.util

Class AbstractQueue

java.lang.Object extended by java.util.AbstractCollection java.util.AbstractQueue

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

Direct Known Subclasses:

ArrayBlockingQueue, ConcurrentLinkedQueue, DelayQueue, LinkedBlockingQueue, 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 ornull 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 aCollection.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

Constructor Summary
protected	AbstractQueue() Constructor for use by subclasses.

Method Summary
boolean	add(E o) Adds the specified element to this queue.
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 collection.
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
contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray, toString

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, [wait](../../java/lang/Object.html#wait%28long, int%29)

Methods inherited from interface java.util.Queue
offer, peek, poll

Methods inherited from interface java.util.Collection
contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray

Constructor Detail

AbstractQueue

protected AbstractQueue()

Constructor for use by subclasses.

Method Detail

add

public boolean add(E o)

Adds the specified element to this queue. This implementation returns true if offer succeeds, else throws an IllegalStateException.

Specified by:

[add](../../java/util/Collection.html#add%28E%29) in interface [Collection](../../java/util/Collection.html "interface in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>

Overrides:

[add](../../java/util/AbstractCollection.html#add%28E%29) in class [AbstractCollection](../../java/util/AbstractCollection.html "class in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>

Parameters:

o - the element

Returns:

true (as per the general contract ofCollection.add).

Throws:

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null

[IllegalStateException](../../java/lang/IllegalStateException.html "class in java.lang") - if element cannot be added

remove

public E remove()

Retrieves and removes the head of this queue. This implementation returns the result of poll unless the queue is empty.

Specified by:

[remove](../../java/util/Queue.html#remove%28%29) 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 element()

Retrieves, but does not remove, the head of this queue. This implementation returns the result of peek unless the queue is empty.

Specified by:

[element](../../java/util/Queue.html#element%28%29) 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 collection. The collection will be empty after this call returns.

This implementation repeatedly invokes poll until it returns null.

Specified by:

[clear](../../java/util/Collection.html#clear%28%29) 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%28%29) 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<? extends E> c)

Adds all of the elements in the specified collection to this queue. Attempts to addAll of a queue to itself result inIllegalArgumentException. 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 collection, 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%28java.util.Collection%29) 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%28java.util.Collection%29) in class [AbstractCollection](../../java/util/AbstractCollection.html "class in java.util")<[E](../../java/util/AbstractQueue.html "type parameter in AbstractQueue")>

Parameters:

c - collection whose elements are to be added to this collection.

Returns:

true if this collection changed as a result of the call.

Throws:

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if the specified collection or any of its elements are null.

[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if c is this queue.

See Also:

add(Object)

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.