Joomla! site syndication http://www.oodesign.com 2010-07-30T15:20:54+01:00 http://www.oodesign.com http://www.oodesign.com/images/M_images/joomla_rss.png text/html 2007-11-11T21:01:47+01:00 http://www.oodesign.com http://www.oodesign.com/mediator-pattern.html Mediator Pattern The mediator pattern is used to takes the role of a hub or router and facilitates the communication between many classes. A similarity can be made with the database systems. The mediator transform a hard to implement relation of many to many, where each calls has to communicate with each other class, in 2 relations, easy to implement, of many to one and one to many, where the communication is handled by the mediator class.In order to have a good object oriented design we have to create lots of classes interacting one with each other. If certain principles are not applied the final framework will end in a total mess where each object relies on many other objects in order to run. In order to avoid tight coupled frameworks, we need this mechanism to facilitate the interaction between objects in a manner in that objects are not aware of the existence of other objects. text/html 2007-02-05T17:41:08+01:00 http://www.oodesign.com http://www.oodesign.com/visitor-pattern.html Visitor PatternMotivationCollections are data types widely used in object oriented programming. Often collections contain objects of different types and in those cases some operations have to be performed on all the collection elements without knowing the type. A possible approach to apply a specific operation on objects of different types in a collection would be the use if blocks in conjunction with 'instanceof' for each element. This approach is not a nice one, not flexible and not object oriented at all. At this point we should think to the Open Close principle and we should remember from there that we can replace if blocks with an abstract class and each concrete class will implement its own operation. text/html 2006-08-23T15:35:50+01:00 http://www.oodesign.com http://www.oodesign.com/template-method-pattern.html Template MethodMotivationIf we take a look at the dictionary definition of a template we can see that a template is a preset format, used as a starting point for a particular application so that the format does not have to be recreated each time it is used. text/html 2006-08-23T16:34:04+01:00 http://www.oodesign.com http://www.oodesign.com/command-pattern.html Command“An object that contains a symbol, name or key that represents a list of commands, actions or keystrokes”. This is the definition of a macro, one that should be familiar to any computer user. From this idea the Command design pattern was given birth. The Macro represents, at some extent, a command that is built from the reunion of a set of other commands, in a given order. Just as a macro, the Command design pattern encapsulates commands (method calls) in objects allowing us to issue requests without knowing the requested operation or the requesting object. Command design pattern provides the options to queue commands, undo/redo actions and other manipulations. text/html 2006-11-21T17:15:33+01:00 http://www.oodesign.com http://www.oodesign.com/strategy-pattern.html StrategyMotivationThere are common situations when classes differ only in their behavior. For this cases is a good idea to isolate the algorithms in separate classes in order to have the ability to select different algorithms at runtime.