AbstractQueue (Java Platform SE 6) (original) (raw)

java.util

Class AbstractQueue

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, 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

AbstractQueue

protected AbstractQueue()

Constructor for use by subclasses.

add

public 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.

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")>

Specified by:

[add](../../java/util/Queue.html#add%28E%29) 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%28E%29) 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))

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 remove()

Retrieves and removes the head of this queue. This method differs from 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%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 method differs from 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%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 queue. The queue 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 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%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 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)

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