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SOLID Principles of Refactoring Presentation - Inland Empire User Group

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Abstract: SOLID is a mnemonic acronym coined by Robert C. Martin (aka Uncle Bob) referring to a collection of design principles of object-oriented programming and design. By using these principles, ...

Abstract: SOLID is a mnemonic acronym coined by Robert C. Martin (aka Uncle Bob) referring to a collection of design principles of object-oriented programming and design. By using these principles, developers are much more likely to create a system that more maintainable and extensible. SOLID can be used to remove code smells by refactoring. In this session, you will learn about the following SOLID principles with code examples demonstrating the corresponding refactoring.

S – Single Responsibility Principle – An Object should have only one reason to change.
O – Open/Closed Principle – A software entity(module, library, routine) should be closed to any modification but be open to extension
L – Liskov Substitution Principle – Derived classes should be substitutable for the base classes
I – Interface Segregation Principle – Having more fine grained interfaces over fat interfaces
D – Dependency Inversion Principle – Depending on abstractions, not concrete implementations.

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SOLID Principles of Refactoring Presentation - Inland Empire User Group SOLID Principles of Refactoring Presentation - Inland Empire User Group Presentation Transcript

  • REFACTORING CODE TO A SOLID FOUNDATION Adnan Masood http://blog.adnanmasood.com @adnanmasood adnanmasood@acm.org Presented at Inland Empire .NET UG – 12/11/2012Slides Courtesy of Steve Smith Pluralsight and Derick Bailey, Los Techies
  • E X A MP L E A P P : B E F O R E A N D AFTER OR HOW TO GET FROM HERE TO THERE? Before AfterCourtesy Steve Smith, PluralSight Training - SOLID Principles of Object Oriented Design
  • CREDITS & REFERENCES• Robert C Martin – Clean Coder https://sites.google.com/site/unclebobconsultingllc/• Pablo’s SOLID Software Development | LosTechies.com Derick Bailey - McLane Advanced Technologies, LLC• PluralSight Training - SOLID Principles of Object Oriented Design http://pluralsight.com/training/Courses/TableOfContents/principles-oo-design• Marcin Zajączkowski - http://solidsoft.wordpress.com/• Images Used Under License• http://www.lostechies.com/blogs/derickbailey/archive/2009/02/11/solid-development-principles-in-motivational- pictures.aspx• SRP Article• http://www.objectmentor.com/resources/articles/srp.pdf• Solid for your Language• http://stefanroock.files.wordpress.com/2011/09/solidforyourlanguage.pdf
  • HELP : ABOUTAdnan Masood works as a system architect / technical lead for Green dot Corporation where hedevelops SOA based middle-tier architectures, distributed systems, and web-applications usingMicrosoft technologies. He is a Microsoft Certified Trainer holding several technicalcertifications, including MCPD (Enterprise Developer), MCSD .NET, and SCJP-II. Adnan isattributed and published in print media and on the Web; he also teaches WindowsCommunication Foundation (WCF) courses at the University of California at San Diego andregularly presents at local code camps and user groups. He is actively involved in the .NETcommunity as cofounder and president of the of San Gabriel Valley .NET Developers group.Adnan holds a Master’s degree in Computer Science; he is currently a doctoral student workingtowards PhD in Machine Learning; specifically discovering interestingness measures in outliersusing Bayesian Belief Networks. He also holds systems architecture certification from MIT andSOA Smarts certification from Carnegie Melon University.
  • ADDITIONAL RESOURCESUncle Bob’s Principle Of Object Oriented Development: http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOodPablo’s Topic Of The Month: SOLID http://www.lostechies.com/blogs/chad_myers/archive/2008/03/07/ pablo-s-topic-of-the-month-march-solid-principles.aspxAgile Principles, Patterns, And Practices In C# by Robert (Uncle Bob) Martin and Micah MartinPablo’s SOLID E-Book http://www.lostechies.com/content/pablo_ebook.aspx
  • OBJECT ORIENTED PRINCIPLES -QUIZ COHESION: “A measure of how strongly-related and focused the various responsibilities of a software module are” - Wikipedia COUPLING: “The degree to which each program module relies on each one of the other modules” – Wikipedia ENCAPSULATION: “The hiding of design decisions in a computer program that are most likely to change” - Wikipedia
  • S.O.L.I.D. PRINCIPLES SRP: SINGLE RESPONSIBILITY PRINCIPLE OCP: OPEN CLOSED PRINCIPLE LSP: LISKOV SUBSTITUTION PRINCIPLE ISP: INTERFACE SEGREGATION PRINCIPLE DIP: DEPENDENCY INVERSION PRINCIPLE
  • THE SINGLE RESPONSIBILITYPRINCIPLE
  • SRP: THE SINGLE RESPONSIBILITYPRINCIPLEThe Single Responsibility Principle states that every objectshould have a single responsibility, and that responsibilityshould be entirely encapsulated by the class. WikipediaThere should never be more than one reason for a class tochange. Robert C. “Uncle Bob” Martin
  • COHESION AND COUPLING Cohesion: how strongly-related and focused are the various responsibilities of a module Coupling: the degree to which each program module relies on each one of the other modulesStrive for low coupling and highcohesion!
  • RESPONSIBILITIES ARE AXES OFCHANGE Requirements changes typically map to responsibilities More responsibilities == More likelihood of change Having multiple responsibilities within a class couples together these responsibilities The more classes a change affects, the more likely the change will introduce errors.
  • Demo The Problem With Too ManyResponsibilities
  • WHAT IS A RESPONSIBILITY?“a reason to change”A difference in usage scenarios from the client’s perspectiveMultiple small interfaces (follow ISP) can help to achieve SRP
  • SRP: SINGLERESPONSIBILITYFILE AND SEND AN EMAIL EXAMPLE APP: READ A FLAT
  • SRP: SINGLE RESPONSIBILITYEXAMPLE APP NEW REQUIREMENTS: SEND FROM NON -WINFORMS APP. READ XML OR FLAT FILE
  • EXAMPLE APP: A BETTER STRUCTURE
  • SUMMARY Following SRP leads to lower coupling and higher cohesion Many small classes with distinct responsibilities result in a more flexible design Related Fundamentals: o Open/Closed Principle o Interface Segregation Principle o Separation of Concerns Recommended Reading: o Clean Code by Robert C. Martin [http://amzn.to/Clean-Code]
  • THE OPEN / CLOSED PRINCIPLE
  • OCP: THE OPEN/CLOSED PRINCIPLEThe Open / Closed Principle states that software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification Wikipedia
  • THE OPEN / CLOSED PRINCIPLEOpen to Extension New behavior can be added in the futureClosed to Modification Changes to source or binary code are not requiredDr. Bertrand Meyer originated the OCP term in his 1988book, Object Oriented Software Construction
  • CHANGE BEHAVIOR WITHOUTCHANGING CODE?Rely on abstractions No limit to variety of implementations of each abstractionIn .NET, abstractions include: Interfaces Abstract Base ClassesIn procedural code, some level of OCP can beachieved via parameters
  • THE PROBLEM Adding new rules require changes to the calculator every time Each change can introduce bugs and requires re-testing, etc. We want to avoid introducing changes that cascade through many modules in our application Writing new classes is less likely to introduce problems o Nothing depends on new classes (yet) o New classes have no legacy coupling to make them hard to design or test
  • THREE APPROACHES TO ACHIEVEOCP Parameters (Procedural Programming) o Allow client to control behavior specifics via a parameter o Combined with delegates/lambda, can be very powerful approach Inheritance / Template Method Pattern o Child types override behavior of a base class (or interface) Composition / Strategy Pattern o Client code depends on abstraction o Provides a “plug in” model o Implementations utilize Inheritance; Client utilizes Composition
  • WHEN DO WE APPLY OCP? Experience Tells You If you know from your own experience in the problem domain that a particular class of change is likely to recur, you can apply OCP up front in your designOtherwise – “Fool me once, shame on you; fool me twice, shame on me” Don’t apply OCP at first If the module changes once, accept it. If it changes a second time, refactor to achieve OCPRemember TANSTAAFL There Ain’t No Such Thing As A Free Lunch OCP adds complexity to design No design can be closed against all changes
  • SUMMARY Conformance to OCP yields flexibility, reusability, and maintainability Know which changes to guard against, and resist premature abstraction Related Fundamentals: o Single Responsibility Principle o Strategy Pattern o Template Method Pattern Recommended Reading: o Agile Principles, Patterns, and Practices by Robert C. Martin and Micah Martin [http://amzn.to/agilepppcsharp]
  • THE LISKOV SUBSTITUTIONPRINCIPLE
  • LSP: THE LISKOV SUBSTITUTIONPRINCIPLEThe Liskov Substitution Principle states thatSubtypes must be substitutable for their basetypes. Agile Principles, Patterns, and Practices in C# Named for Barbara Liskov, who first described the principle in 1988.
  • SUBSTITUTABILITYChild classes must not:1) Remove base class behavior2) Violate base class invariantsAnd in general must not require calling code to know they aredifferent from their base type.
  • INHERITANCE AND THE IS-ARELATIONSHIPNaïve OOP teaches use of IS-A to describe child classes’relationship to base classesLSP suggests that IS-A should be replaced withIS-SUBSTITUTABLE-FOR
  • LSP: LISKOV SUBSTITUTIONPRINCIPLE EXAMPLE APP: VIOLATING LSP WITH DATABASE CONNECTION INFO
  • LSP: LISKOV SUBSTITUTIONPRINCIPLE EXAM PL E APP: CO RRECTI NG FO R LSP – M O VE THE DAT AB A SE RE ADE R
  • INVARIANTS Consist of reasonable assumptions of behavior by clients Can be expressed as preconditions and postconditions for methods Frequently, unit tests are used to specify expected behavior of a method or class Design By Contract is a technique that makes defining these pre- and post-conditions explicit within code itself. To follow LSP, derived classes must not violate any constraints defined (or assumed by clients) on the base classes
  • THE PROBLEM Non-substitutable code breaks polymorphism Client code expects child classes to work in place of their base classes “Fixing” substitutability problems by adding if- then or switch statements quickly becomes a maintenance nightmare (and violates OCP)
  • LSP VIOLATION “SMELLS”foreach (var emp in Employees){ if( emp is Manager ) { _printer.PrintManager( emp as Manager ); } else { _printer.PrintEmployee( emp ); }}
  • LSP VIOLATION “SMELLS”public abstract class Base{ Follow ISP! public abstract void Method1(); public abstract void Method2(); Use small interfaces so you} don‟t require classes topublic class Child : Base implement more than they{ need! public override void Method1() { throw new NotImplementedException(); } public override void Method2() { // do stuff }}
  • WHEN DO WE FIX LSP?If you notice obvious smells like those shownIf you find yourself being bitten by the OCP violations LSP invariably causes
  • LSP TIPS “Tell, Don’t Ask” o Don’t interrogate objects for their internals – move behavior to the object o Tell the object what you want it to do Consider Refactoring to a new Base Class o Given two classes that share a lot of behavior but are not substitutable… o Create a third class that both can derive from o Ensure substitutability is retained between each class and the new base
  • SUMMARY Conformance to LSP allows for proper use of polymorphism and produces more maintainable code Remember IS-SUBSTITUTABLE-FOR instead of IS-A Related Fundamentals: o Polymorphism o Inheritance o Interface Segregation Principle o Open / Closed Principle Recommended Reading: o Agile Principles, Patterns, and Practices by Robert C. Martin and Micah Martin [http://amzn.to/agilepppcsharp]
  • THE INTERFACE SEGREGATIONPRINCIPLE
  • ISP: THE INTERFACE SEGREGATIONPRINCIPLEThe Interface Segregation Principle statesthat Clients should not be forced to dependon methods they do not use. Agile Principles, Patterns, and Practices in C#Corollary: Prefer small, cohesive interfaces to “fat” interfaces
  • WHAT’S AN INTERFACE?Interface keyword/type public interface IDoSomething { … }Public interface of a class public class SomeClass { … }What does the client see and use?
  • ISP: INTERFACESEGREGATION THE DISADVANTAGES OF “THIS PRINCIPLE DEALS WITHPRINCIPLECLASSES CLASSESINTERFACES „FAT‟ „FAT‟ INTERFACES. INTERFACES ARE WHOSE THAT HAVE ARE NOT COHESIVE. IN OTHER WORDS, THE INTERFACES OF THE CLASS CAN BE BROKEN UP INTO GROUPS OF MEMBER FUNCTIONS. EACH GROUP SERVES A DIFFERENT SET OF CLIENTS. THUS SOME CLIENTS USE ONE GROUP OF MEMBER FUNCTIONS, AND OTHER CLIENTS USE THE OTHER GROUPS.” - ROBERT MARTIN
  • Demo
  • ISP: INTERFACESEGREGATIONPRINCIPLEEXAMPLE APP: CLARIFYING THE EMAIL SENDER AND MESSAGE INFO PARSING
  • THE PROBLEMClient Class (Login Control) Needs This:
  • THE PROBLEM AboutPage simply needs ApplicationName and AuthorName Forced to deal with huge ConfigurationSettings class Forced to deal with actual configuration filesInterface Segregation violations result in classes that depend onthings they do not need, increasing coupling and reducingflexibility and maintainability
  • ISP SMELLS Unimplemented interface methods:public override string ResetPassword( string username, string answer) { throw new NotImplementedException(); }Remember these violate Liskov Substitution Principle!
  • ISP SMELLSClient references a class but only uses small portion of it
  • WHEN DO WE FIX ISP? Once there is pain o If there is no pain, there’s no problem to address. If you find yourself depending on a “fat” interface you own o Create a smaller interface with just what you need o Have the fat interface implement your new interface o Reference the new interface with your code If you find “fat” interfaces are problematic but you do not own them o Create a smaller interface with just what you need o Implement this interface using an Adapter that implements the full interface
  • ISP TIPS Keep interfaces small, cohesive, and focused Whenever possible, let the client define the interfaceWhenever possible, package the interface with the client o Alternately, package in a third assembly client and implementation both depend upon o Last resort: Package interfaces with their implementation
  • SUMMARY Don’t force client code to depend on things it doesn’t need Keep interfaces lean and focused Refactor large interfaces so they inherit smaller interfaces Related Fundamentals: o Polymorphism o Inheritance o Liskov Substitution Principle o Façade Pattern Recommended Reading: o Agile Principles, Patterns, and Practices by Robert C. Martin and Micah Martin [http://amzn.to/agilepppcsharp]
  • THE DEPENDENCY INVERSIONPRINCIPLE
  • DIP: DEPENDENCY INVERSIONPRINCIPLE “WHAT IS IT THAT MAKES A DESIGN RIGID, FRAGILE AND IMMOBILE? IT IS THE INTERDEPENDENCE OF THE MODULES WITHIN THAT DESIGN. A DESIGN IS RIGID IF IT CANNOT BE EASILY CHANGED. SUCH RIGIDITY IS DUE TO THE FACT THAT A SINGLE CHANGE TO HEAVILY INTERDEPENDENT SOFTWARE BEGINS A CASCADE OF CHANGES IN DEPENDENT MODULES.” - ROBERT MARTIN
  • DIP: THE DEPENDENCY INVERSIONPRINCIPLEHigh-level modules should not depend onlow-level modules. Both should depend onabstractions.Abstractions should not depend on details.Details should depend on abstractions. o Agile Principles, Patterns, and Practices in C#
  • DIP: DEPENDENCYINVERSIONPRINCIPLE
  • DIP: DEPENDENCYINVERSIONPRINCIPLE
  • DIP: DEPENDENCYINVERSIONPRINCIPLE
  • DIP:DEPENDENCYINVERSIONPRINCIPLE
  • DIP: DEPENDENCY INVERSION PRINCIPLEEXAMPLE APP: CONSTRUCTOR DEPENDENCIES IN A PROCESSING SERVICE
  • WHAT ARE DEPENDENCIES? Framework Third Party Libraries Database File System Email Web Services System Resources (Clock) Configuration The new Keyword Static methods Thread.Sleep Random
  • TRADITIONAL PROGRAMMING ANDDEPENDENCIES High Level Modules Call Low Level Modules User Interface depends on o Business Logic depends on o Infrastructure o Utility o Data Access Static methods are used for convenience or as Façade layers Class instantiation / Call stack logic is scattered through all modules o Violation of Single Responsibility Principle
  • CLASS DEPENDENCIES: BE HONEST! Class constructors should require any dependencies the class needs Classes whose constructors make this clear have explicit dependencies Classes that do not have implicit, hidden dependencies public class HelloWorldHidden { public string Hello(string name) { if (DateTime.Now.Hour < 12) return "Good morning, " + name; if (DateTime.Now.Hour < 18) return "Good afternoon, " + name; return "Good evening, " + name; } }
  • CLASSES SHOULD DECLARE WHATTHEY NEEDpublic class HelloWorldExplicit { private readonly DateTime _timeOfGreeting; public HelloWorldExplicit(DateTime timeOfGreeting) { _timeOfGreeting = timeOfGreeting; } public string Hello(string name) { if (_timeOfGreeting.Hour < 12) return "Good morning, " + name; if (_timeOfGreeting.Hour < 18) return "Good afternoon, " + name; return "Good evening, " + name; }}
  • THE PROBLEM Order has hidden dependencies: o MailMessage o SmtpClient o InventorySystem o PaymentGateway o Logger o DateTime.Now Result o Tight coupling o No way to change implementation details (OCP violation) o Difficult to test
  • DEPENDENCY INJECTION Dependency Injection is a technique that is used to allow calling code to inject the dependencies a class needs when it is instantiated. The Hollywood Principle o “Don’t call us; we’ll call you” Three Primary Techniques o Constructor Injection o Property Injection o Parameter Injection Other methods exist as well
  • CONSTRUCTOR INJECTION Dependencies are passed in via constructorStrategy Pattern Pros o Classes self-document what they need to perform their work o Works well with or without a container o Classes are always in a valid state once constructed Cons o Constructors can have many parameters/dependencies (design smell) o Some features (e.g. Serialization) may require a default constructor o Some methods in the class may not require things other methods require (design smell)
  • PROPERTY INJECTION Dependencies are passed in via a property o Also known as “setter injection” Pros o Dependency can be changed at any time during object lifetime o Very flexible Cons o Objects may be in an invalid state between construction and setting of dependencies via setters o Less intuitive
  • PARAMETER INJECTION Dependencies are passed in via a method parameter Pros o Most granular o Very flexible o Requires no change to rest of class Cons o Breaks method signature o Can result in many parameters (design smell) Consider if only one method has the dependency, otherwise prefer constructor injection
  • REFACTORINGExtract Dependencies into InterfacesInject implementations of interfaces into OrderReduce Order’s responsibilities (apply SRP)
  • DIP SMELLS Use of new keywordforeach(var item in cart.Items){ try { var inventorySystem = new InventorySystem(); inventorySystem.Reserve(item.Sku, item.Quantity); }}
  • DIP SMELLSUse of static methods/propertiesmessage.Subject = "Your order placed on " +DateTime.Now.ToString();OrDataAccess.SaveCustomer(myCustomer);
  • WHERE DO WE INSTANTIATEOBJECTS? Applying Dependency Injection typically results in many interfaces that eventually need to be instantiated somewhere… but where? Default Constructor o You can provide a default constructor that news up the instances you expect to typically need in your application o Referred to as “poor man’s dependency injection” or “poor man’s IoC” Main o You can manually instantiate whatever is needed in your application’s startup routine or main() method IoC Container o Use an “Inversion of Control” Container
  • IOC CONTAINERS Responsible for object graph instantiation Initiated at application startup via code or configuration Managed interfaces and the implementation to be used are Registered with the container Dependencies on interfaces are Resolved at application startup or runtime Examples of IoC Containers for .NET o Microsoft Unity o StructureMap o Ninject o Windsor o Funq / Munq
  • SUMMARY Depend on abstractions. Don’t force high-level modules to depend on low-level modules through direct instantiation or static method calls Declare class dependencies explicitly in their constructors Inject dependencies via constructor, property, or parameter injection Related Fundamentals: o Single Responsibility Principle o Interface Segregation Principle o Façade Pattern o Inversion of Control Containers Recommended Reading: o Agile Principles, Patterns, and Practices by Robert C. Martin and Micah Martin [http://amzn.to/agilepppcsharp] o http://www.martinfowler.com/articles/injection.html
  • TRADITIONAL (NAÏVE) LAYEREDARCHITECTURE
  • INVERTED ARCHITECTURE
  • THE PROBLEM Dependencies Flow Toward Infrastructure Core / Business / Domain Classes Depend on Implementation Details Result o Tight coupling o No way to change implementation details without recompile (OCP violation) o Difficult to test
  • DEPENDENCY INJECTION Dependency is transitive o If UI depends on BLL depends on DAL depends on Database Then *everything* depends on the Database Depend on abstractions (DIP) Package interfaces (abstractions) with the client (ISP) Structure Solutions and Projects so Core / BLL is at center, with fewest dependencies
  • SUMMARY Don’t Depend on Infrastructure Assemblies from Core Apply DIP to reverse dependencies Related Fundamentals: o Open Closed Principle o Interface Segregation Principle o Strategy Pattern Recommended Reading: o Agile Principles, Patterns, and Practices by Robert C. Martin and Micah Martin [http://amzn.to/agilepppcsharp] o http://www.martinfowler.com/articles/injection.html
  • DON’T REPEAT YOURSELF“Every piece of knowledge must have a single, unambiguousrepresentation in the system.” The Pragmatic Programmer“Repetition in logic calls for abstraction. Repetition in processcalls for automation.” 97 Things Every Programmer ShouldKnowVariations include: Once and Only Once Duplication Is Evil (DIE)
  • ANALYSIS Magic Strings/Values Duplicate logic in multiple locations Repeated if-then logic Conditionals instead of polymorphism Repeated Execution Patterns Lots of duplicate, probably copy-pasted, code Only manual tests Static methods everywhere
  • MAGIC STRINGS / VALUES
  • DUPLICATE LOGIC IN MULTIPLELOCATIONS
  • REPEATED IF-THEN LOGIC
  • CONDITIONAL INSTEAD OFPOLYMORPHISM  Example of Flags Over Objects anti-pattern  Violates the Tell, Don’t Ask principle (aka DIP)
  • SUMMARY Repetition breeds errors and waste Refactor code to remove repetition Recommended Reading: o The Pragmatic Programmer: From Journeyman to Master http://amzn.to/b2gJdK o 97 Things Every Programmer Should Know http://amzn.to/cAse1Y
  • STATIC METHODS Tightly coupled Difficult to test Difficult to change behavior (violates OCP) Cannot use object oriented design techniques o Inheritance o Polymorphism
  • SUMMARY Repetition breeds errors and waste Abstract repetitive logic in code Related Fundamentals: o Template Method Pattern o Command Pattern o Dependency Inversion Principle Recommended Reading: o The Pragmatic Programmer: From Journeyman to Master http://amzn.to/b2gJdK o 97 Things Every Programmer Should Know http://amzn.to/cAse1Y
  • REPEATED EXECUTION PATTERNS
  • DUPLICATE, COPY PASTED CODEToo Numerous to ListCommercial Tool (free version available) o Atomiq (http://GetAtomiq.com)
  • CONSIDER CODE GENERATION T4 Templates o Custom code generation templates o Built into Visual Studio 2010 ORM Tools (LINQ to SQL, Entity Framework, nHibernate, LLBLGen) o Reduce repetitive data access code o Eliminate common data access errors Commercial Tools: o CodeSmith o CodeBreeze o CodeHayStack
  • REPETITION IN PROCESS Testing o Performing testing by hand is tedious and wasteful Builds o Performing builds by hand is tedious and wasteful Deployments o Performing deployments by hand is tedious and wasteful Are you seeing a trend here? String.Format(“Performing {0} by hand is tedious and wasteful”, action);
  • SUMMARY Repetition breeds errors and waste Use an ORM tool to eliminate repeated data access code Use Tools to Locate Repeated Code Automate repetitive actions in your processes Recommended Reading: o The Pragmatic Programmer: From Journeyman to Master http://amzn.to/b2gJdK o 97 Things Every Programmer Should Know http://amzn.to/cAse1Y Related Tool o Atomiq http://GetAtomiq.com
  • E X A MP L E A P P : B E F O R E A N DS.O.L.I.D. CONVERSION SUMMARY AFTER Before After
  • S.O.L.I.D. -> OO LOW COUPLING: OCP, DIP, ISPPRINCIPLES
  • S.O.L.I.D. -> OO H IGH C OH E S ION : L OW C OU P L IN G + S R P , L S PPRINCIPLES
  • S.O.L.I.D. -> OO PRINCIPLES ENCAPSULATION: SRP, LSP, DIP
  • QUESTIONS?
  • THANK YOU!Adnan Masoodadnanmasood@acm.org @adnanmasood Blog: blog.AdnanMasood.com Pasadena .NET User Group: www.sgvdotnet.org