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Design Patterns For 70% Of Programmers In The World


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Design Patterns For 70% Of Programmers In The World

  1. 1. Design Patterns for 70% of genious programmers Aamir Khan Solution Architect
  2. 2. Design Patterns for 70% of programmers in the world Saurabh Verma Solution Architect I blog at
  3. 3. Agenda <ul><li>Do you OOPs? </li></ul><ul><li>Design Patterns? Why </li></ul><ul><li>Design Patterns? What </li></ul><ul><li>Design Patterns? How </li></ul><ul><li>I hate my job </li></ul>
  4. 4. Normal Classes vs Abstract Classes vs Interfaces Normal Class: This is a normal class  Abstract Class: These cannot be instantiated directly. They may provide partial implementations and exists solely for the purpose of inheritance. Interfaces: Defines a contract. Concrete implementations needs to implement each property and method as per contract. Shut up ! We know all this
  5. 5. Million Dollar Question? What is Why?
  6. 6. Normal Class vs Abstract Class? If a particular class is a entity which is not required to be instantiated by the application directly, go for Abstract Class Employee can be abstract class
  7. 7. Abstract Class vs Interfaces? If a particular class contains any default behavior, go for Abstract Class If every concrete class has its own implementation, go for Interfaces Work – Management, Programming
  8. 8. MOVIES & ACTORS Shahrukh Khan Salman Khan riding bike Actors in a Movie
  9. 9. IS-A vs HAS-A vs CAN-DO IS-A Inheritance Shahrukh Khan is an ACTOR HAS-A Composition Movie has ACTORS CAN-DO Interfaces Salman Khan can DRIVE BIKE IS-A Inheritance Shahrukh Khan is an ACTOR HAS-A Composition Movie has ACTORS CAN-DO Interfaces Salman Khan can DRIVE BIKE
  10. 10. What is a Pattern <ul><li>An 'element of reusable software’ </li></ul><ul><li>A design pattern systematically names, motivates, and explains a general design that addresses a recurring design problem in object-oriented systems. </li></ul><ul><li>It describes the problem, the solution, when to apply the solution, and its consequences. </li></ul><ul><li>It also gives implementation hints and examples. The solution is a general arrangement of objects and classes that solve the problem. The solution is customized and implemented to solve the problem in a particular context. </li></ul>
  11. 11. History of Software Patterns
  12. 12. What Wikipedia says, <ul><li>A design pattern is a general repeatable solution to a commonly occurring problem in software design. </li></ul><ul><li>A design pattern is not a finished design that can be transformed directly into code. </li></ul><ul><li>Algorithms are not thought of as design patterns. </li></ul>
  13. 13. Let’s understand design patterns by purpose
  14. 14. Let’s understand the purpose + Creational Patterns Structural Patterns Final Product Behavioral Patterns
  15. 15. Let’s understand the purpose
  16. 16. Design Patterns as per their PURPOSE
  17. 17. Creational Patterns
  18. 18. Factory Method
  19. 19. Factory Method <ul><li>Define an interface for creating an object, but let subclass decide which class to instantiate </li></ul><ul><li>Prevents creation of any additional instances, while simultaneously allowing global access </li></ul><ul><li>Creation can be delayed until it is actually required </li></ul>
  20. 20. Factory Method System.Data.SqlClient.SqlClientFactory
  21. 21. Abstract Factory Pattern
  22. 22. Abstract Factory Pattern <ul><li>Provide an interface for creating families of related or dependent objects without specifying their concrete classes. </li></ul><ul><li>Provides creation of families of related or dependent objects without specifying their concrete class </li></ul>
  23. 23. Abstract Factory Method System.Data.Common.DbProviderFactories
  24. 24. Singleton Pattern
  25. 25. Singleton Pattern <ul><li>Ensure a class has only one instance, and provide a global point to it. </li></ul><ul><li>Prevents creation of any additional instances, while simultaneously allowing global access </li></ul><ul><li>Creation can be delayed until it is actually required </li></ul>
  26. 26. Singleton Pattern System.Data.SqlClient.SqlClientFactory
  27. 27. Structural Patterns
  28. 28. Façade Pattern
  29. 29. Façade Pattern <ul><li>Provide a unified interface to set of interfaces in a subsystem. </li></ul><ul><li>Is generally one side of the exterior of a building, especially the front </li></ul><ul><li>Origin from a FRENCH word means “face” or “front” </li></ul>
  30. 30. Façade Pattern Its all about the service
  31. 31. Decorator Pattern
  32. 32. Decorator Pattern <ul><li>Attach additional responsibilities to an object dynamically. </li></ul><ul><li>Flexible alternative to subclassing for extending functionality </li></ul><ul><li>Allows dynamic and transparent addition and removal of responsibilities without affecting object </li></ul>simple actress ( act ) in role of modern girl (go out and act ) in role of homely girl (be in home and act )
  33. 33. Decorator Pattern System.IO.BufferedStream:Stream
  34. 34. Composite Pattern
  35. 35. Composite Pattern <ul><li>Compose objects into tree structures to represent part-whole hierarchies </li></ul><ul><li>When dealing with collections of objects, there are often operations that are appropriate for both a single object and the entire collection </li></ul><ul><li>Treats individual objects and composition of objects uniformly </li></ul><ul><li>Example: </li></ul><ul><li>Every object “IS-A” shape </li></ul><ul><li>Every shape “HAS-A” draw behavior </li></ul>
  36. 36. Composite Pattern System.Web.UI.Control (Render Mechanism)
  37. 37. Composite Pattern
  38. 38. Adapter Pattern
  39. 39. Adapter Pattern <ul><li>Convert the interface of a class into another interface clients expect </li></ul><ul><li>Lets classes work together that couldn’t work otherwise </li></ul><ul><li>Works good for making compliance </li></ul>Application Framework Adapter Legacy Component
  40. 40. Adapter Pattern GearsTypelib.HtmlDialogHostClass (Interop.GearsTypelib)
  41. 41. Decorator vs Adapter Decorator looks like Adapter which “decorates” an existing class to make it compatible. Though, Decorator doesn’t wants you to decorate every method in the Adapted class. But who has stopped from doing it. “ Never underestimate the power of a developer”
  42. 42. Decorator vs Façade Façade is a way of hiding a complex system inside a simpler interface, whereas Decorator adds function by wrapping a class.
  43. 43. Behavioural Patterns
  44. 44. Command Pattern
  45. 45. Command Pattern <ul><li>Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests. </li></ul><ul><li>If all commands can service a specific request, they can be entertained by the invoker </li></ul><ul><li>Concrete command performs the action on Receiver </li></ul><ul><li>Encapsulate method invocation </li></ul>One Receiver and Multiple actions
  46. 46. Command Pattern System.ComponentModel.Design.MenuCommand
  47. 47. Command Pattern Saurabh.Learning.DesignPatterns.Patterns.CommandPattern
  48. 48. Strategy Pattern
  49. 49. Strategy Pattern <ul><li>Define strategies for a performing a behavior and change them dynamically as per requirement </li></ul><ul><li>This lets the algorithm vary independently from clients that uses it </li></ul><ul><li>It is about choice, which affects outcomes </li></ul>
  50. 50. Strategy Pattern System.Collections.ArrayList
  51. 51. Template Method
  52. 52. Template Method <ul><li>Define the skeleton of an algorithm in an operations, deferring some steps to subclass </li></ul><ul><li>Main algorithm skeleton is defined in a base class and subclasses can then plug in their own details without affecting the algorithm itself </li></ul><ul><li>Uses Inheritance – Abstract Class defines the template (algorithm) and Concrete class manages the implementation. </li></ul><ul><li>Template uses the implementation on demand </li></ul>
  53. 53. Template Method
  54. 54. Strategy Pattern vs Template Method <ul><li>Strategy allows callers to change the algorithm or order of steps whereas Template method allow steps to be modified </li></ul><ul><li>Strategy uses Interfaces whereas Template method uses Inheritance </li></ul>
  55. 55. I hate my job
  57. 57. Reflect when you want 
  58. 58. Answers, anybody?
  59. 59. CONTENT STOLEN FROM  BOOKS: Head First Design Patterns Design Patterns in C# Design Patterns WEBSITES: Wikipedia, MSDN, doFactory and GOOGLE
  60. 60. Learn it all, at my blog Don’t contact me at, [at] Saurabh Verma Solution Architect