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Topic: Observer pattern

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	Observer (Microsoft Patterns) (Site not responding. Last check: 2007-09-15)
		Allowing observers to be notified only when an event related to their specific interest occurs reduces the dependency chain and helps to avoid infinite loops.
		This feature is useful in scenarios where the number of observers is not known at design time (for example, if you need an observer for each window that the user opens in the application).
		If observers are used extensively throughout an application, it becomes nearly impossible for a developer to understand what is happening by looking at the source code.
	msdn.microsoft.com /library/en-us/dnpatterns/html/DesObserver.asp?frame=true (2501 words)

	Learn more about Design pattern (computer science) in the online encyclopedia. (Site not responding. Last check: 2007-09-15)
		Design patterns represent the accumulated knowledge of the community of software developers of standardised solutions to recurring problems.
		A design pattern is an abstraction of a solution for a particular class of problems.
		It is important that patterns accompany a name because it makes possible to describe problems, solutions and talk about them with other folks.
	www.onlineencyclopedia.org /d/de/design_pattern__computer_science_.html (515 words)

	Applying and Extending the Observer Pattern in THRSim11.
		This heavy use of the observer pattern resulted in an application that consists of several components or modules which are loosely coupled together.
		The use of this observer framework is easier than the use of the original observer pattern.
		Using this extended observer framework within the simulator and for developing external components, it will be possible to connect external server components run-time to the client application (the simulator) using the observer design pattern as a coupling mechanism.
	www.hc11.demon.nl /thrsim11/ddj/article.htm (5762 words)

	Design Patterns Project - Example
		A design pattern has a name, a description of the problem it addresses, and a general solution that designers must tailor to their particular variant of the problem.
		If Subject and Observer are lumped together, then the resulting object must either span two layers (and violate the layering), or it must be forced to live in one layer or the other (which might compromise the layering abstraction).
		ChangeManager is an instance of the Mediator (273) pattern.
	researchweb.watson.ibm.com /designpatterns/example.htm (2589 words)

	Enterprise Java Community: Spring Loaded Observer Pattern (Site not responding. Last check: 2007-09-15)
		Although the Factory Pattern and the Singleton Pattern are built into Spring, other patterns such as the Decorator Pattern, the Adapter Pattern, and the Observer Pattern are often forgotten because of the new ideas Spring has to offer.
		The pattern is useful when you have one publisher and many subscribers (one-to-many) that are interested in the publisher's state or messages.
		The intimate details of the Observer Pattern are far outside of the scope of this article, but a note worthy topic is how the Spring framework can be used to leverage good object oriented design techniques while creating the concrete classes of this pattern.
	www.theserverside.com /articles/article.tss?l=SpringLoadedObserverPattern (1294 words)

	Observer
		Whenever the Subject changes, it broadcasts to all registered Observers that it has changed, and each Observer queries the Subject for that subset of the Subject's state that it is responsible for monitoring.
		The Observer pattern captures the lion's share of the Model-View-Controller architecture that has been a part of the Smalltalk community for years.
		Observer defines a very decoupled interface that allows for multiple receivers to be configured at run-time.
	home.earthlink.net /~huston2/dp/observer.html (449 words)

	ASPN : Python Cookbook : Observer Pattern (Site not responding. Last check: 2007-09-15)
		This is a Python implementation of the observer pattern described by Gamma et.
		Observer was a kind of interface that documented the behaviour of an observer.
		I disagree, forcing observers to be subclassed from an IObserver class is unecessary.
	aspn.activestate.com /ASPN/Cookbook/Python/Recipe/131499 (294 words)

	Design Pattern Summary: Observer (Site not responding. Last check: 2007-09-15)
		The Observer is a powerful pattern to implement when applied appropriately; however, this may not always be the case.
		Another problem that can occur with this pattern is that during the path of notification the Subject's state may be modified in a multi-threaded environment, so by having the ConcreteObserver retrieve the Subject's state in the notification may cause either the old state or the new state to be retrieved.
		To enable the behavior to be consistent pass the changed values into the notification to the Observers and not have the Observers reference the Subject at all.
	pages.cpsc.ucalgary.ca /~phong/courses/SENG609.04/Observer.htm (547 words)

	[No title] (Site not responding. Last check: 2007-09-15)
		If we put this information into the observers, the most harmful consequence would be a data redundancy that would grow in proportional way to the quantity of additional information (backgrounds) and the quantity of interfaces.
		The Middle Observer Pattern’s main disadvantage is: It must be implemented the entire subject’s messages in the MiddleObserver class; this produce plenty of forwarding messages that just delegate the same request to the model and few of them could be useful for a MiddleObserver object.
		Mediator Pattern: The idea of having an object in the middle of an application that intercepts all the update requests and broadcasts them to other objects doing some extra tasks where is needed and encapsulates how they interacts, make us think in a Mediator Pattern.
	jerry.cs.uiuc.edu /~plop/plop98/final_submissions/P48.doc (1564 words)

	design:observer_pattern [phpPatterns]
		The Observer Pattern is designed to help cope with one to many relationships between objects, allowing changes in an object to update many associated objects.
		Conceptually, the Observer pattern in something like a trigger in a database, which runs a stored procedure when a table row is modified for example (we won’t go too far with this analogy though).
		Notice in the construction of Observer, it is passed a reference to an instance of Observable then calls the addObserver() method in Observable to register itself as a “watching” object.
	www.phppatterns.com /docs/design/observer_pattern (1473 words)

	On Using the Observer Design Pattern
		I have tried to avoid repeating things about the pattern already described in [1], the reader should be familiar with the particular section.
		The observer design pattern supports such dependencies and at the same time tries to reduce the coupling between the object that changes (the subject) and the object that needs a change notification (the observer).
		In the implementation section of the Observer pattern [1], a ChangeManager is introduced.
	www.wohnklo.de /patterns/observer.html (3751 words)

	Observer Design Pattern
		The Observer pattern defines an one-to-many dependency between a subject object and any number of observer objects so that when the subject object changes state, all its observer objects are notified and updated automatically.
		An example of using the observer pattern is the graphical interface toolkit which separates the presentational aspect with application data.
		SpreadSheetFormula, BarGraph, and PieChart are the observer objects.
	sern.ucalgary.ca /courses/SENG/609.04/W98/lamsh/observerLib.html (1123 words)

	observer Design Pattern application (Site not responding. Last check: 2007-09-15)
		Patterns can be used as documentation, to ensure that components stay decoupled and variabilities remain flexible.
		Equip the observers with an interface for receiving the notifications from the subject.
		Languages based on constraints generally do not use the Observer pattern, because local propagation is inefficient for complex constraints and is susceptible to cycles.
	coweb.cc.gatech.edu /cs2340/463 (1613 words)

	Keeping Objects In Sync
		One such pattern is known as the Observer pattern, which is a solution to the updating problem that arises when some objects have a dependency relationship with others.
		The Observer pattern provides a way for each of the views to be notified whenever the subject has changed, without requiring that the subject know anything about the views, other than that they are observers.
		Whenever an observer registers with a subject, it is done with respect to an aspect of that subject.
	java.sun.com /developer/technicalArticles/Programming/KeepObjectsInSync (2090 words)

	The Observer Pattern (Site not responding. Last check: 2007-09-15)
		Whether this behaviour was modelled correctly on the Observer pattern or not, the result is that several 'interested parties' got to know about a change in the content of the project that we are working on.
		If you are not comfortable with using interfaces, which is the simplest way of implementing the Observer pattern, then you need to use Composition to supply the necessary additional functionality to existing classes.
		The Clock Observer class derives from TObserver and overrides the Update method to check if the Subject being passed is indeed a TClockTimer and then passes that Clock Timer to the ObserverUpdate method of the Digital Clock.
	blogs.teamb.com /joannacarter/articles/690.aspx (2547 words)

	CSimpleObservable - An Implementation of the Observer pattern in JavaScript
		Observers and Observables are a basic pattern in event-based programming.
		Synchronous observerables are useful when observers must be notified of each distinct change using the observer's current state.
		Asynchronous observables are useful when only the notification is important and the exact state of the observable at the time is not required.
	devedge-temp.mozilla.org /toolbox/examples/2003/CSimpleObservable/index_en.html (287 words)

	ONDotnet.com: Using the Observer Pattern in .NET
		Design pattern purists will be quick to note that this application does not use every feature of an Observer pattern.
		Design patterns serve as a blueprint for reusable code, but should be flexible for the needs of an individual application.
		The Observer pattern seems to appear in many cases throughout the framework.
	www.ondotnet.com /pub/a/dotnet/2005/01/03/binaryclock.html (1998 words)

	The Event Generator Idiom
		The observer pattern is one of 23 design patterns described in the book Design Patterns: Elements of Reusable Object-Oriented Software by Gamma, Helm, Johnson, and Vlissides (aka the Gang of Four).
		But with a design pattern, both the problem and solution are generic enough to be independent of implementation language.
		For example, a design pattern might describe a way to ensure there is only one instance of a class (the singleton pattern).
	www.artima.com /designtechniques/eventgen.html (561 words)

	ONJava.com: Reducing Upgrade Risk with Aspect Oriented Programming
		Observer design pattern and upgrade a subclass method via AOP.
		The Observer pattern (also known as publish-subscribe) is useful for designing code with a single server and multiple client classes.
		has three methods that allow observers to be added, removed, and notified (the notify is used for updating observer data).
	www.onjava.com /pub/a/onjava/2005/03/16/aop-mgmt.html (743 words)

	Observer Design Pattern
		This Observer pattern is based on the Observer pattern as described in [Gam+, pages 293..303].
		In terms of the observer pattern the object dispatching an event is called subject, the object handling the event is called observer.
		In response each observer may query the subject to synchronise its state with the subject’s state’ [Gam+, p 294].
	www.castle-cadenza.demon.co.uk /observe.htm (600 words)

	Synchronize Data Among Objects with the Publish/Subscribe Design Pattern
		This design pattern is a variation of the Observer pattern (see Figure 1) described in Design Patterns, Elements of Reusable Object Oriented Software, a work many consider the original design patterns book.
		In the Observer pattern, an object (the Observer) registers to listen for events from another object (the Subject); the Observer is implicitly aware of the Subject.
		Also, whereas in Observer the events come only from a specific source, in Publish/Subscribe any object that is aware of the Event Channel may publish an event.
	www.devx.com /enterprise/article/7976 (462 words)

	[No title] (Site not responding. Last check: 2007-09-15)
		One of the most important ways to improve this paper is to clarify the relationship between your pattern and the Observer pattern as quickly as possible.
		It seems that one difference between the Event Notification pattern and the Observer pattern is the ability to transparently add filtering between Subject and Observer.
		This would also help to explain if/how the Event Notification pattern is truly a new pattern, or if it's just a different "mutation" of the Observer pattern that has grown up in a different environment and thus has different external characteristics (but a similar core).
	www.cs.wustl.edu /~schmidt/papers/TAPOS/event-notification.review (1218 words)

	Dave Burke : The Observer Pattern
		The Observer pattern is how you coordinate multiple UI views of the same set of data.
		We use the observer pattern to wire up the various observers of the subject data.
		So now, whenever the observers change the state of the subject, all other observers are affected.
	dbvt.com /blog/archive/2005/06/25/2657.aspx (1143 words)

	Multicast
		Multicast is a pattern in progress, assuming it's a pattern at all.
		Observer partitions that object to give you flexibility, etc. Observer worries little about the information that passes between them or the extensibility thereof---it focuses on notification and subject-observer consistency.
		A many-to-one dependency can be viewed as multiple degenerate applications of the pattern; that is, many-to-one is just a collection of subject-observer pairs all sharing the same observer.
	www.research.ibm.com /designpatterns/pubs/multicast.html (3045 words)

	CS635: Doc 7, Observer
		Java's observer interface is the Observer abstract class in the pattern
		Notifies all observers of the specified observable change which occurred.
		Each time a counter changes value, it notifies its observers of the type of change.
	www.eli.sdsu.edu /courses/spring98/cs635/notes/observer/observer.html (974 words)

	Publish and Subscribe Using C++ and the Observer Pattern (Site not responding. Last check: 2007-09-15)
		The observer pattern provides a simple but powerful model for achieving this crucial design goal.
		A design pattern called the observer pattern was created [1] to accommodate this type of scenario and a C++ realization of it is the topic of this article.
		Using patterns allows us to stand on the shoulders of giants as we try to engineer the software solutions of today and tomorrow.
	www.informit.com /articles/article.asp?p=390393 (396 words)

	Observer Design Pattern
		The intent of the Observer dsign pattern is to "define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically."
		The "observers" subscribe to the subject and are therefore notified by the subject when the data changes.
		This is a design pattern because it is often wise to separate differents aspects of an abstraction.
	www.ship.edu /~cawell/patterns/2observer.htm (631 words)

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