Software Design Principles
- 1. Software Design Principles Navigator Internal Workshop
- 2. Old Story Clean Simple Elegant Rigid Fragile Immobile Change with Requirement Out-of-Control Dependencies
- 3. Solution Software Development = Complexity Management Change with Requirement and Follow Principles OCP LSP DIP ISP Clean Simple Elegant Huge but still Clean Simple Elegant
- 4. Open Close Principle (OCP) A module should be Open for Extension but Close for Modification Solution: Polymorphism
- 5. Liskov Substitution Principle (LSP) Subclasses should be Substitutable for their Base Classes
- 6. Liskov Substitution Principle (LSP) Root Cause: Is-A Fails Solution: Design by Contract Method pre-condition in subclass shouldn’t be stronger than in base class Method post-condition in subclass shouldn’t be weaker than in base class
- 7. Dependency Inversion Principle (DIP) Depend upon Abstractions. Don't depend upon Concretions. The Last Mile: Where to instantiate the concrete class?
- 8. Interface Segregation Principle (ISP) Many client specific interfaces are better than one general purpose interface
- 9. Summary Less Responsibilities in a Interface/Class Dependencies on Outside Classes More Abstraction to act as Dependency Firewall Small Single-Responsibility Class to Encapsulate Change Manage Complexity = Manage Dependencies Clean Simple Elegant Clean Simple Elegant Clean Simple Elegant Clean Simple Elegant Clean Simple Elegant
- 10. More Principles Package Cohesion Principles REP: Release Reuse Equivalency Principle CCP: Common Closure Principle CRP: Common Reuse Principle Package Coupling Principles ACP: Acyclic Dependencies Principle SDP: Stable Dependencies Principle SAP: Stable Abstractions Principle
- 11. Thank you
Editor's Notes
- #2: Opening customized for each location