org.erights.e.elib.vat
Class Queue

java.lang.Object
  |
  +--org.erights.e.elib.vat.Queue

All Implemented Interfaces:

Enumeration

Direct Known Subclasses:

SynchQueue

public class Queue

extends Object

implements Enumeration

Safe: A conventional fifo queue in which dequeued items are removed in the same order they were enqueued.

An untyped queue can hold any object (except null). A queue can be created with a dynamic type, in which case, at no extra overhead, enqueue will only enqueue objects of that type (or a subtype, but not null). This check imposes no *extra* overhead, since java always makes us pay for a dynamic type check on array store anyway.

The class Queue itself is no longer thread safe, instead being optimized for using inside one vat. See the subclass SynchQueue for a thread-safe variant with a blocking operation.

Author:

Mark S. Miller

See Also:

org.erights.e.elib.vat.Vat

Field Summary

private static int	INITIAL_SIZE
private int	myCurSize
private int	myIn
private int	myMaxSize
private int	myOut
private Object[]	myStuff

Constructor Summary

Queue()
Enabled: Makes a Queue that can hold any object.

Queue(Class elementType)
Enabled: Makes a Queue that can hold objects of the specified elementType.

Method Summary

void	enqueue(Object newElement) Enabled: Add a new element to the queue.
boolean	hasMoreElements() Enabled: Check to see if the queue has more elements.
Object	nextElement() Enabled: Get the least-recently-added element off of the queue.
Object	optDequeue() Enabled: Get the least-recently-added element off of the queue, or null if the queue is currently empty.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Enumeration

asList, iterate

Field Detail

INITIAL_SIZE

private static final int INITIAL_SIZE

myStuff

private Object[] myStuff

myMaxSize

private int myMaxSize

myCurSize

private int myCurSize

myOut

private int myOut

myIn

private int myIn

Constructor Detail

Queue

public Queue()

Enabled: Makes a Queue that can hold any object.

Queue

public Queue(Class elementType)

Enabled: Makes a Queue that can hold objects of the specified elementType.

Parameters:

elementType - may not be a primitive (ie, scalar) type.

Method Detail

enqueue

public void enqueue(Object newElement)

Enabled: Add a new element to the queue.

Parameters:

newElement - the object to be added to the end of the queue.

Throws:

NullPointerException - thrown if newElement is null

ArrayStoreException - thrown if newElement does not coerce to the elementType specified in the Queue constructor.

hasMoreElements

public boolean hasMoreElements()

Enabled: Check to see if the queue has more elements. This method allows a Queue to be used as an Enumeration.

Specified by:

hasMoreElements in interface Enumeration

Returns:

is false if the queue is empty, otherwise true

nextElement

public Object nextElement()
                   throws NoSuchElementException

Enabled: Get the least-recently-added element off of the queue. If the queue is currently empty, throw NoSuchElementException. This method allows a Queue to be used as an Enumeration.

Specified by:

nextElement in interface Enumeration

Returns:

the next element of this enumeration.

NoSuchElementException

optDequeue

public Object optDequeue()

Enabled: Get the least-recently-added element off of the queue, or null if the queue is currently empty.