SOLID - Open Closed Principle

Transcript

1. Open/Closed Principle
2. Single Responsibility!
3. Session Objectives and Takeaways  OCP Definition by Bertrand Meyer & Robert C. Martin  Understand the Problem and various Code Smells  How OCP comes to the rescue?  Understand Fundamental Concepts  Exception scenarios for OCP Principle  How to refactor your code using OCP?
4. Software entities should be open for extension, but closed for modification
5. Open for Extension Closed for Modification Must be able to satisfy changing requirements and support new features. Must be able to extend behavior without editing existing code.
6. Once a class is deployed to Production or other clients start using it, you should not make changes to that class.
7. Once a class is done, it is done!
8. Why will this small enhancement take so much time? Development is simple But Testing will take time
9. Code Smells which OCP tries to resolve RIGIDITY FRAGILITY IMMOBILITY
11. RED GREEN REFACTOR Write a failing unit test recreating the bug Modify existing code so that unit test passes. Enhance the code without changing behavior. Defects/Bug Fixes TDD
12. Client Awareness Change is allowed to a class as long as it does not require change to any client using it. Loose Coupling Tight Coupling
13. Open for Extension
14. Extension Points
15. Types of Extension Points Implementation Inheritance Interface Inheritance Rely on Abstractions – Abstract Base Classes and Interfaces
16. Virtual Methods A lass that arks o e of its e ers as virtual is Ope to E te sio . Virtual methods have an implementation but can be overridden in the derived class. Virtual method Abstract method Can provide a default implementation. Cannot have an implementation. If it is good enough, Child classes can use it or else override it. Child class must give their own implementation. Can exist on abstract or non- abstract class. Can only exist on an abstract class.
17. Why Abstract Class? Move the common functionalities into the Base class. You do not want the base class to be instantiated. Code Maintainability is easier.
18. public class Person Behavior - Jump public class Monkey : Person Behavior – Person Writes Code Behavior – Monkey Writes Code ?? public class Monkey
19. Multiple Class Inheritance CLASS A CLASS B CLASS C CLASS D DIAMOND PROBLEM
20. Why Interfaces? Interfaces are purely abstract – no implementation, only declarations. Interfaces describe functionality whereas Class describes traits. Interfaces separate definition of objects from its implementation. Interfaces helps to develop loosely coupled systems. X Y X Y Interface
22. Open Closed Principle – Benefits E isting fun tionalit won’t reak No need to change working code No need to fix broken unit tests New classes have no legacy coupling, hence less likely to create issues Move changes to Production faster. Build code that allows changes over time