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Showing posts from November, 2011

Design Pattern : behavioural

Chain of responsibility The purpose for this is for high cohesion. This means, to increase the reusability. This can be visualized with the specialization in manufacturing world. Each function performs specialized task, and chained together to perform a bigger task. These functions can be reused in other scope since they are doing specialized and simpler task. Command This is to encapsulate requests. Thus, for a program to call any command, it has the similar interface. Interpreter This will translate the context passed by client and perform necessary task on it. Iterator This to enable to parse through the whole data structure. Mediator As a middle man between 2 sub-program to enable low coupling, or for decoupling purpose. Momento This is to capture the state of the class and stored in another object Good for undo to restore the object to its previous state Observer It’s for event driven. As listener, or “don’t call me, I’ll call you”  (After reading the online not

Design Pattern : structural

Composite It looks like tree structure, the end node is called leaf. All the node has uniform interface, thus they can be used/called via uniform operation/data structure Adaptor This is using another class to encapsulate the class to be accessed. Thus the caller will see/use the same interface regardless on how the class to be assessed being implemented. proxy This is acting as a middle man to handle the client requests and sever response. Façade This is using an interface to reduce the complexity. It packages the objects and methods Decorator This is for dynamically to add new responsibility / variation on the methods It will hold the base class pointer, and the real implementation on the child class or actual object. Bridge This is acting like multi-purpose adapter. It serves for multi-platform. Flyweight It handles the pool of resources that are shared by the clients. Private Class Data This is to put the private and readonly data into a class, and being initial

Design Pattern : creation

Singleton this is basically suitable for single instance through out the program. it can contains the static variables used by the program. the benefits for this versus global variable is for data encapsulation purpose. You can have accessor and modifier functions as a guarding to set or read the variable. Factory The factory is a class to hold and control the creation of the class objects. The object class held by factory is the base class, thus any of the child class object can be instantiated, and transparent in the main program. Abstract Factory Similar to Factory type, but the factory is an abstract class. This is good for multi-platform support, where the right factory will be instantiated based on the platform. Builder This is to hide the complexity of the object by the builder. The program can have multiple builder with same operation but different methods. There is a “directory” to call the right builder to call for operation to produce “product”. Protot

OO concept and software development practices

I attended a 5-day Design Pattern class last year, and the summary that I published then, was the initial thought of this k-db site. I am revising them and put them here. :) Day 1 : OO concept and software development practices OO concept revised. Normally these are discussed : inheritance composition encapsulation polymorphism Discussed in class : abstraction encapsulation generalization specialization Type of errors compilation syntax contextual linking runtime logical Example to show the best way to code to avoid error : if (x == 0) if (0 == x) <– using this coding style, missing a "=" in the condition statement will alarm error during compilation. Why it is a good practice to use static for variable declaration? for information hiding. so people won’t use extern to access to it in other file, to ensure the value is not overwritten by unknown. error prone during linking. Software quality measurement : reusability : code, function, user exper