org.datanucleus.store.types.backed

Class Queue

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue

org.datanucleus.store.types.simple.Queue

org.datanucleus.store.types.backed.Queue

All Implemented Interfaces:

Serializable, Cloneable, Iterable, Collection, Queue, BackedSCO, SCO, SCOCollection, SCOContainer, SCOMtoN

public class Queue
extends Queue
implements BackedSCO

A mutable second-class Queue object. This class extends AbstractQueue, using that class to contain the current objects, and the backing CollectionStore to be the interface to the datastore. A "backing store" is not present for datastores that dont use DatastoreClass, or if the container is serialised or non-persistent.

Modes of Operation

The user can operate the list in 2 modes. The cached mode will use an internal cache of the elements (in the "delegate") reading them at the first opportunity and then using the cache thereafter. The non-cached mode will just go direct to the "backing store" each call.

Mutators

When the "backing store" is present any updates are passed direct to the datastore as well as to the "delegate". If the "backing store" isn't present the changes are made to the "delegate" only.

Accessors

When any accessor method is invoked, it typically checks whether the container has been loaded from its "backing store" (where present) and does this as necessary. Some methods (size()) just check if everything is loaded and use the delegate if possible, otherwise going direct to the datastore.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	allowNulls
protected ListStore	backingStore
protected boolean	isCacheLoaded
protected boolean	queued
protected boolean	useCache

Fields inherited from class org.datanucleus.store.types.simple.Queue

delegate, LOCALISER, ownerMmd, ownerOP

Constructor Summary

Constructors

Constructor and Description
Queue(ObjectProvider op, AbstractMemberMetaData mmd) Constructor.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	add(Object element) Method to add an element to the Collection.
boolean	addAll(Collection elements) Method to add a collection of elements.
void	clear() Method to clear the Collection.
Object	clone() Creates and returns a copy of this object.
boolean	contains(Object element) Accessor for whether an element is contained in the Collection.
boolean	containsAll(Collection c) Accessor for whether a collection of elements are contained here.
boolean	equals(Object o) Equality operator.
Store	getBackingStore()
Object	getValue() Accessor for the unwrapped value that we are wrapping.
int	hashCode() Hashcode operator.
void	initialise() Method to initialise the SCO for use.
void	initialise(Object o, boolean forInsert, boolean forUpdate) Method to initialise the SCO from an existing value.
boolean	isEmpty() Accessor for whether the Collection is empty.
boolean	isLoaded() Method to return if the SCO has its contents loaded.
Iterator	iterator() Accessor for an iterator for the Collection.
void	load() Method to effect the load of the data in the SCO.
protected void	loadFromStore() Method to load all elements from the "backing store" where appropriate.
boolean	offer(Object element) Method to offer an element to the Queue.
Object	peek() Method to peek at the next element in the Queue.
Object	poll() Method to poll the next element in the Queue.
boolean	remove(Object element) Method to remove an element from the Collection.
boolean	remove(Object element, boolean allowCascadeDelete) Method to remove an element from the collection, and observe the flag for whether to allow cascade delete.
boolean	removeAll(Collection elements) Method to remove a Collection of elements.
boolean	retainAll(Collection c) Method to retain a Collection of elements (and remove all others).
int	size() Accessor for the size of the Collection.
Object[]	toArray() Method to return the Collection as an array.
Object[]	toArray(Object[] a) Method to return the Collection as an array.
String	toString() Method to return the Collection as a String.
void	unsetOwner() Method to unset the owner and field information.
void	updateEmbeddedElement(Object element, int fieldNumber, Object value) Method to update an embedded element in this collection.
protected Object	writeReplace() The writeReplace method is called when ObjectOutputStream is preparing to write the object to the stream.

Methods inherited from class org.datanucleus.store.types.simple.Queue

attachCopy, detachCopy, getFieldName, getOwner, initialiseDelegate, makeDirty

Methods inherited from class java.util.AbstractQueue

element, remove

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

backingStore

protected transient ListStore backingStore

allowNulls

protected transient boolean allowNulls

useCache

protected transient boolean useCache

isCacheLoaded

protected transient boolean isCacheLoaded

queued

protected transient boolean queued

Constructor Detail

Queue

public Queue(ObjectProvider op,
     AbstractMemberMetaData mmd)

Constructor.

Parameters:

op - The ObjectProvider for this set.

mmd - Metadata for the member

Method Detail

initialise

public void initialise(Object o,
              boolean forInsert,
              boolean forUpdate)

Method to initialise the SCO from an existing value.

Specified by:

initialise in interface SCO

Overrides:

initialise in class Queue

Parameters:

o - The object to set from

forInsert - Whether the object needs inserting in the datastore with this value

forUpdate - Whether to update the datastore with this value

initialise

public void initialise()

Method to initialise the SCO for use.

Specified by:

initialise in interface SCO

Overrides:

initialise in class Queue

getValue

public Object getValue()

Accessor for the unwrapped value that we are wrapping.

Specified by:

getValue in interface SCO

Overrides:

getValue in class Queue

Returns:

The unwrapped value

load

public void load()

Method to effect the load of the data in the SCO. Used when the SCO supports lazy-loading to tell it to load all now.

Specified by:

load in interface SCOContainer

Overrides:

load in class Queue

isLoaded

public boolean isLoaded()

Method to return if the SCO has its contents loaded. If the SCO doesn't support lazy loading will just return true.

Specified by:

isLoaded in interface SCOContainer

Overrides:

isLoaded in class Queue

Returns:

Whether it is loaded

loadFromStore

protected void loadFromStore()

Method to load all elements from the "backing store" where appropriate.

getBackingStore

public Store getBackingStore()

Specified by:

getBackingStore in interface BackedSCO

updateEmbeddedElement

public void updateEmbeddedElement(Object element,
                         int fieldNumber,
                         Object value)

Method to update an embedded element in this collection.

Specified by:

updateEmbeddedElement in interface SCOCollection

Overrides:

updateEmbeddedElement in class Queue

Parameters:

element - The element

fieldNumber - Number of field in the element

value - New value for this field

unsetOwner

public void unsetOwner()

Method to unset the owner and field information.

Specified by:

unsetOwner in interface SCO

Overrides:

unsetOwner in class Queue

clone

public Object clone()

Creates and returns a copy of this object.

Mutable second-class Objects are required to provide a public clone method in order to allow for copying PersistenceCapable objects. In contrast to Object.clone(), this method must not throw a CloneNotSupportedException.

Specified by:

clone in interface SCO

Overrides:

clone in class Queue

Returns:

A clone of the object

contains

public boolean contains(Object element)

Accessor for whether an element is contained in the Collection.

Specified by:

contains in interface Collection

Specified by:

contains in interface SCOMtoN

Overrides:

contains in class Queue

Parameters:

element - The element

Returns:

Whether the element is contained here

containsAll

public boolean containsAll(Collection c)

Accessor for whether a collection of elements are contained here.

Specified by:

containsAll in interface Collection

Overrides:

containsAll in class Queue

Parameters:

c - The collection of elements.

Returns:

Whether they are contained.

equals

public boolean equals(Object o)

Equality operator.

Specified by:

equals in interface Collection

Overrides:

equals in class Queue

Parameters:

o - The object to compare against.

Returns:

Whether this object is the same.

hashCode

public int hashCode()

Hashcode operator.

Specified by:

hashCode in interface Collection

Overrides:

hashCode in class Queue

Returns:

The Hash code.

isEmpty

public boolean isEmpty()

Accessor for whether the Collection is empty.

Specified by:

isEmpty in interface Collection

Overrides:

isEmpty in class Queue

Returns:

Whether it is empty.

iterator

public Iterator iterator()

Accessor for an iterator for the Collection.

Specified by:

iterator in interface Iterable

Specified by:

iterator in interface Collection

Overrides:

iterator in class Queue

Returns:

The iterator

peek

public Object peek()

Method to peek at the next element in the Queue.

Specified by:

peek in interface Queue

Overrides:

peek in class Queue

Returns:

The element

size

public int size()

Accessor for the size of the Collection.

Specified by:

size in interface Collection

Overrides:

size in class Queue

Returns:

The size

toArray

public Object[] toArray()

Method to return the Collection as an array.

Specified by:

toArray in interface Collection

Overrides:

toArray in class Queue

Returns:

The array

toArray

public Object[] toArray(Object[] a)

Method to return the Collection as an array.

Specified by:

toArray in interface Collection

Overrides:

toArray in class Queue

Parameters:

a - The array to write the results to

Returns:

The array

toString

public String toString()

Method to return the Collection as a String.

Overrides:

toString in class AbstractCollection

Returns:

The string form

add

public boolean add(Object element)

Method to add an element to the Collection.

Specified by:

add in interface Collection

Specified by:

add in interface Queue

Overrides:

add in class Queue

Parameters:

element - The element to add

Returns:

Whether it was added successfully.

addAll

public boolean addAll(Collection elements)

Method to add a collection of elements.

Specified by:

addAll in interface Collection

Overrides:

addAll in class Queue

Parameters:

elements - The collection of elements to add.

Returns:

Whether they were added successfully.

clear

public void clear()

Method to clear the Collection.

Specified by:

clear in interface Collection

Overrides:

clear in class Queue

offer

public boolean offer(Object element)

Method to offer an element to the Queue.

Specified by:

offer in interface Queue

Overrides:

offer in class Queue

Parameters:

element - The element to offer

Returns:

Whether it was added successfully.

poll

public Object poll()

Method to poll the next element in the Queue.

Specified by:

poll in interface Queue

Overrides:

poll in class Queue

Returns:

The element (now removed)

remove

public boolean remove(Object element)

Method to remove an element from the Collection.

Specified by:

remove in interface Collection

Overrides:

remove in class Queue

Parameters:

element - The Element to remove

Returns:

Whether it was removed successfully.

remove

public boolean remove(Object element,
             boolean allowCascadeDelete)

Method to remove an element from the collection, and observe the flag for whether to allow cascade delete.

Specified by:

remove in interface SCOCollection

Overrides:

remove in class Queue

Parameters:

element - The element

allowCascadeDelete - Whether to allow cascade delete

Returns:

Whether it was removed successfully.

removeAll

public boolean removeAll(Collection elements)

Method to remove a Collection of elements.

Specified by:

removeAll in interface Collection

Overrides:

removeAll in class Queue

Parameters:

elements - The collection to remove

Returns:

Whether they were removed successfully.

retainAll

public boolean retainAll(Collection c)

Method to retain a Collection of elements (and remove all others).

Specified by:

retainAll in interface Collection

Overrides:

retainAll in class Queue

Parameters:

c - The collection to retain

Returns:

Whether they were retained successfully.

writeReplace

protected Object writeReplace()
                       throws ObjectStreamException

The writeReplace method is called when ObjectOutputStream is preparing to write the object to the stream. The ObjectOutputStream checks whether the class defines the writeReplace method. If the method is defined, the writeReplace method is called to allow the object to designate its replacement in the stream. The object returned should be either of the same type as the object passed in or an object that when read and resolved will result in an object of a type that is compatible with all references to the object.

Overrides:

writeReplace in class Queue

Returns:

the replaced object

Throws:

ObjectStreamException