_templates.javolution.context

Class PersistentContext.Reference

java.lang.Object

_templates.javolution.context.PersistentContext.Reference

All Implemented Interfaces:

Reference

Enclosing class:

PersistentContext

public static class PersistentContext.Reference
extends Object
implements Reference

This class represents a reference over an object which can be kept persistent accross multiple program executions. Instances of this class are typically used to hold global data time consuming to regenerate. For example:[code] public class FastMap implements Map { // Provides a constructor for persistent maps. public FastMap(String id) { new PersistentContext.Reference(id, this) { protected void notifyChange() { FastMap.this.clear(); FastMap.this.putAll(this.get()); } }; } } ... // Persistent lookup table for units multiplications. static FastMap> UNITS_MULT_LOOKUP = new FastMap>("UNITS_MULT_LOOKUP").shared(); [/code]

Persistent references may also be used to hold optimum configuration values set from previous executions. For example:[code] public Targets { private static PersistentContext.Reference CAPACITY = new PersistentContext.Reference("Targets#CAPACITY", 256); private Target[] _targets = new Target[CAPACITY.get()]; private int _count; public void add(Target target) { if (_count == _targets.length) { // Ooops, resizes. Target[] tmp = new Target[_count * 2]; System.arraycopy(_targets, 0, tmp, 0, _count); _targets = tmp; CAPACITY.setMinimum(_targets.length); // Persists. } _targets[_count++] target; } }[/code]

Version:

4.0, September 4, 2006

Author:

Jean-Marie Dautelle

Constructor Summary

Constructors

Constructor and Description
Reference(String id, Object defaultValue) Creates a persistent reference identified by the specified name and having the specified default value.

Method Summary

Modifier and Type	Method and Description
Object	get() Returns the value this reference referes to.
protected void	notifyChange() Notifies this reference that its value has changed (for example a new persistent context has been loaded).
void	set(Object value) Sets the value this reference referes to.
void	setMaximum(Object value) Sets this reference to the specified value only if (value.compareTo(this.get()) < 0).
void	setMinimum(Object value) Sets this reference to the specified value only if (value.compareTo(this.get()) > 0).
String	toString() Returns the string representation of the current value of this reference.

Methods inherited from class java.lang.Object

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

Constructor Detail

Reference

public Reference(String id,
                 Object defaultValue)

Creates a persistent reference identified by the specified name and having the specified default value.

Parameters:

id - the unique identifier.

defaultValue - the default value.

Throws:

IllegalArgumentException - if the name is not unique.

Method Detail

get

public Object get()

Description copied from interface: Reference

Returns the value this reference referes to.

Specified by:

get in interface Reference

Returns:

the referent or null if not set.

set

public void set(Object value)

Description copied from interface: Reference

Sets the value this reference referes to.

Specified by:

set in interface Reference

Parameters:

value - the reference value.

setMinimum

public void setMinimum(Object value)

Sets this reference to the specified value only if (value.compareTo(this.get()) > 0).

Parameters:

value - the minimum value for this reference.

Throws:

IllegalArgumentException - if the specified value is not Comparable or an Integer instance (J2ME).

setMaximum

public void setMaximum(Object value)

Sets this reference to the specified value only if (value.compareTo(this.get()) < 0).

Parameters:

value - the maximum value for this reference.

Throws:

IllegalArgumentException - if the specified value is not Comparable or an Integer instance (J2ME).

toString

public String toString()

Returns the string representation of the current value of this reference.

Overrides:

toString in class Object

Returns:

String.valueOf(this.get())

notifyChange

protected void notifyChange()

Notifies this reference that its value has changed (for example a new persistent context has been loaded). The default implementation does nothing.