javolution.context

Class PersistentContext.Reference<T>

java.lang.Object

javolution.context.PersistentContext.Reference<T>

All Implemented Interfaces:

Reference<T>

Enclosing class:

PersistentContext

public static class PersistentContext.Reference<T>
extends java.lang.Object
implements Reference<T>

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:

     public class FastMap<K,V> implements Map<K, V> {
         // Provides a constructor for persistent maps.
         public FastMap(String id) {
             new PersistentContext<Map<K, V>.Reference(id, this) {
                  protected void notifyChange() {
                      FastMap.this.clear();
                      FastMap.this.putAll(this.get());
                  }
             };
         }
     }
     ...
     // Persistent lookup table for units multiplications.
     static FastMap<Unit, FastMap<Unit, Unit>> UNITS_MULT_LOOKUP
          =  new FastMap<Unit, FastMap<Unit, Unit>>("UNITS_MULT_LOOKUP").shared();
    

Persistent references may also be used to hold optimum configuration values set from previous executions. For example:

     public Targets {
          private static PersistentContext.Reference<Integer> CAPACITY
               = new PersistentContext.Reference<Integer>("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;
         }
     }

Version:

4.0, September 4, 2006

Author:

Jean-Marie Dautelle

Constructor Summary

Constructors

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

Method Summary

Modifier and Type	Method and Description
T	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(T value) Sets the value this reference referes to.
void	setMaximum(T value) Sets this reference to the specified value only if (value.compareTo(this.get()) < 0).
void	setMinimum(T value) Sets this reference to the specified value only if (value.compareTo(this.get()) > 0).
java.lang.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(java.lang.String id,
                 T 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:

java.lang.IllegalArgumentException - if the name is not unique.

Method Detail

get

public T get()

Description copied from interface: Reference

Returns the value this reference referes to.

Specified by:

get in interface Reference<T>

Returns:

the referent or null if not set.

set

public void set(T value)

Description copied from interface: Reference

Sets the value this reference referes to.

Specified by:

set in interface Reference<T>

Parameters:

value - the reference value.

setMinimum

public void setMinimum(T value)

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

Parameters:

value - the minimum value for this reference.

Throws:

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

setMaximum

public void setMaximum(T value)

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

Parameters:

value - the maximum value for this reference.

Throws:

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

toString

public java.lang.String toString()

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

Overrides:

toString in class java.lang.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.