edu.emory.mathcs.backport.java.util
public abstract class AbstractQueue extends AbstractCollection implements Queue
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 which does not permit insertion of null elements, along with methods Queue, Queue, 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.
Since: 1.5
Constructor Summary | |
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protected | AbstractQueue()
Constructor for use by subclasses. |
Method Summary | |
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boolean | add(Object 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 c)
Adds all of the elements in the specified collection to this
queue. |
void | clear()
Removes all of the elements from this queue.
|
Object | element()
Retrieves, but does not remove, the head of this queue. |
Object | remove()
Retrieves and removes the head of this queue. |
This implementation returns true if offer succeeds, else throws an IllegalStateException.
Parameters: e the element to add
Returns: true (as specified by Collection#add)
Throws: 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
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.
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 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
See Also: add
This implementation repeatedly invokes poll
until it
returns null.
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.
Returns: the head of this queue
Throws: NoSuchElementException if this queue is empty
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.
Returns: the head of this queue
Throws: NoSuchElementException if this queue is empty