org.perfectjpattern.core.api.behavioral.observer
Interface IObserver<E>

Type Parameters:

E - Type of event data that this IObserver subscribes to.

All Known Subinterfaces:

IClock

All Known Implementing Classes:

AnalogClock, DigitalClock, ObserverProxy

public interface IObserver<E>

Observer Design Pattern: Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. (Gamma et al, Design Patterns)

Responsibility: Abstract generic definition of the "Observer". pattern role.

• Defines an updating interface for objects that should be notified of changes in a subject.

Notes: Improves over the original GoF recipe and Java Observer implementation in that:

• Push over Pull approach: IObserver instances are not coupled to the ISubject interface i.e. there is no need for the IObserver to query ISubject's state. State change or Message content is pushed to the update(E) callback method.
• Strongly typed generic parameter eliminates the need for IObserver to downcast the parameter as is the case for e.g. java.util.Observer implementation.

Example usage:

    //
    // Create Observer Pattern elements 
    //  
    ISubject mySubject = new ConcreteSubject();
    IObserver myFirstObserver = new ConcreteObserver();
    IObserver mySecondObserver = new ConcreteObserver();
    
    //
    // Subscribe multiple Observer instances to the Subject
    //
    mySubject.attach(myFirstObserver, mySecondObserver);
    
    //
    // Notify all subscribed Observers, optionally pass some Event 
    // data associated with the Event.
    //
    mySubject.notifyObservers(NullEventData.getInstance());
    
    //
    // Detach Observer instances
    //
    mySubject.detach(myFirstObserver);
 

Version:

$Revision: 1.0 $ $Date: Jun 11, 2007 6:16:01 AM $

Author:

Giovanni Azua

Method Summary

void	update(E anEventData) Notification from ISubject instance that a change has ocurred.

Method Detail

update

void update(E anEventData)

Notification from ISubject instance that a change has ocurred.

Parameters:

anEventData - Event data pushed to IObserver instances.