FactoryMethod

Factory Method Design Pattern defines an interface for creating an object but lets subclasses decide which class to instantiate. This pattern lets a class defer instantiation to subclasses

Overview

The Factory Method pattern is a creational design pattern that provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created. It promotes loose coupling by eliminating the need to bind application-specific classes into the code.

Implementation Details

This implementation demonstrates a document creation system where different types of documents create their specific pages:

Key Components:

• Document (Creator): Abstract class that declares the factory method CreatePages()
• Page (Product): Abstract base class for all page types
• Concrete Creators: Resume and Report classes that implement CreatePages()
• Concrete Products: Various page types like SkillsPage, EducationPage, IntroductionPage, etc.

Classes:

• Document - Abstract creator with factory method CreatePages() and Pages collection
• Page - Abstract product base class
• Resume - Concrete creator that creates Skills, Education, and Experience pages
• Report - Concrete creator that creates Introduction, Results, Conclusion, Summary, and Bibliography pages
• Page implementations: SkillsPage, EducationPage, ExperiencePage, IntroductionPage, ResultsPage, ConclusionPage, SummaryPage, BibliographyPage

Usage Example:

Document[] documents = new Document[2];
documents[0] = new Resume();  // Creates Skills, Education, Experience pages
documents[1] = new Report();  // Creates Introduction, Results, Conclusion, Summary, Bibliography pages

foreach (Document document in documents)
{
    Console.WriteLine(document.GetType().Name + "--");
    foreach (Page page in document.Pages)
    {
        Console.WriteLine(" " + page.GetType().Name);
    }
}

Benefits:

• Eliminates tight coupling between creator and concrete products
• Follows Single Responsibility Principle - object creation is separated from business logic
• Follows Open/Closed Principle - easy to add new document types without modifying existing code
• Provides flexibility in object creation through inheritance
• Each subclass can create objects appropriate to its context