com.persistit.ref

Class AbstractWeakReference

java.lang.Object

com.persistit.ref.AbstractWeakReference

All Implemented Interfaces:

PersistitReference, Serializable

public abstract class AbstractWeakReference
extends Object
implements PersistitReference

An abstract superclass for implementations of PersistitReference that implement weak reference semantics. A concrete subclass implements the method:

      public Object lookup(Object id)
 

which should return the Object associated with the supplied id, or null if there is none. The meaning of the identifier, and the mechanism used to look up and deserialize the associated object (the referent), are implementation-specific.

This implementation differs from AbstractReference in that the referent object is referenced through a java.lang.ref.WeakReference. Thus the garbage collector may choose to discard the referent value, in which case the get method will simply look it up again on demand.

Version:

1.0

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected Object	_id
protected boolean	_knownNull
protected WeakReference	_weakReference

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AbstractWeakReference() No-arg constructor supplied for object serialization/deserialization.
protected	AbstractWeakReference(Object id) Construct a reference using the persistent identity of an object.
protected	AbstractWeakReference(Object id, Object referent) Construct a reference to the referent Object with the supplied persistent identifier.

Method Summary

Modifier and Type	Method and Description
Object	get() Gets the referent object.
protected abstract Object	lookup(Object id) Look up and instantiate an object using its persistent identifier.

Methods inherited from class java.lang.Object

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

Field Detail

_id

protected Object _id

_weakReference

protected transient WeakReference _weakReference

_knownNull

protected boolean _knownNull

Constructor Detail

AbstractWeakReference

protected AbstractWeakReference()

No-arg constructor supplied for object serialization/deserialization.

AbstractWeakReference

protected AbstractWeakReference(Object id,
                                Object referent)

Construct a reference to the referent Object with the supplied persistent identifier. For correct operation, the referent Object must be equivalent to the object that would result from invoking lookup on the persistent identifier. the object that would be returned by the lookup

Parameters:

id - The persistent identifier. The value of the id must be associated with a unique referent object, and must be stable over time.

referent - The object identified by the id

AbstractWeakReference

protected AbstractWeakReference(Object id)

Construct a reference using the persistent identity of an object. A subsequent invocation of the get method will cause the object to be looked up and instantiated.

Parameters:

id -

Method Detail

get

public Object get()

Gets the referent object. If the object has already been looked up, or if this reference was created using the two-argument constructor, then this merely returns the object. Otherwise this method attempts to look up and instantiate the object using its persistent identifier.

Specified by:

get in interface PersistitReference

Returns:

The referent object.

lookup

protected abstract Object lookup(Object id)

Look up and instantiate an object using its persistent identifier. Typically this will be done by setting up a Exchange and fetching its value.

Parameters:

id - The identifier

Returns:

The referent object.