Open Closed Principle kata

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Talk and Kata on using the Open Closed principal of SOLID as well as Dependency Inversion to complete the Bowling Kata

Talk and Kata on using the Open Closed principal of SOLID as well as Dependency Inversion to complete the Bowling Kata

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  • 1. SOLID The Open/Closed Principle Dependency Inversion Paul Blundell @Blundell_apps www.blundellapps.com
  • 2. Five basic principles of object-orientated programming. “The principles when applied together intend to make it more likely that a programmer will create a system that is easy to maintain and extend over time” S ? O ? L ? I ? D ? SOLID
  • 3. Five basic principles of object-orientated programming. “The principles when applied together intend to make it more likely that a programmer will create a system that is easy to maintain and extend over time” Single Responsibility Principle Open / Closed Principle Liskov’s Substitution Interface Segregation Dependency Inversion SOLID
  • 4. Five basic principles of object-orientated programming. “The principles when applied together intend to make it more likely that a programmer will create a system that is easy to maintain and extend over time” Single Responsibility Principle Open / Closed Principle Liskov’s Substitution Interface Segregation Dependency Inversion SOLID
  • 5. Open / Closed Principle ? SOLID
  • 6. Open / Closed Principle “Software entities (classes, modules, methods etc) should be open for extension but closed for modification” That is such an entity can allow its behaviour to be changed without altering its source code. SOLID
  • 7. Open Closed Principle
  • 8. Open Closed Principle
  • 9. Dependency Inversion
  • 10. The aim of the OCP kata is to use the Open Closed Principle to design a maintainable and extensible code base. Think about: - How to compose functionality out of existing objects - How to avoid reworking existing code OCP Kata
  • 11. Write the first failing test Then write a factory that returns an object or a composed object that makes the test pass. Rules: - the factory should be limited to creating and linking objects - no conditionals allowed in the factory OCP Kata
  • 12. @Test public void scoreZeroForGutterGame() { // First test } @Test public void scoreTwentyForAllOnesGame() { // Second test } // Continue Bowling OCP Kata
  • 13. Write the next failing test Can you make this test pass by just changing the factory and object composite? Yes - Great do it! No - Refactor until you can The refactoring should be the system to a state where it’s possible to implement the next test just by changing the composite of objects that is returned by the factory. Do not implement new functionality when refactoring the current test must still fail. OCP Kata
  • 14. Fork / Clone this repo: git@github.com:novoda/dojos.git Goto this folder: github.com/novoda/dojos/tree/master/ocpBowling Make a copy of this folder (rename default with a team name): github.com/novoda/dojos/tree/master/ocpBowling/20130918-default Rules are in the repo here: ocpBowling/20130918-default/src/main/java/com/bowling/bowling_rules.txt Start! OCP Kata
  • 15. Matteo Vaccari - invented the OCP Kata - http://matteo.vaccari.name/blog/archives/293 David Nicolette - created the OCP jigsaw diagram Uncle Bob - Creator of the original bowling Kata - http://butunclebob.com/ArticleS.UncleBob.TheBowlingGameKata Kevin Rutherford - guided me in the art of Kata’s - http://silkandspinach.net/ Jonas Gauffin - for the meme - http://blog.gauffin.org/2012/05/solid-principles-with-real-world-examples/#.UjWDy9K_s2k Credits Paul Blundell @Blundell_apps www.blundellapps.com