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Coding Dojo Object Calisthenics (2016)
Peter Kofler is a software developer and code mentor who helps development teams improve code quality through mentoring techniques like pair programming and coding dojos. The document summarizes Object-Oriented Programming concepts like abstraction, encapsulation, polymorphism, and inheritance. It also describes "Object Calisthenics" rules for writing high-quality object-oriented code, such as wrapping primitives, short methods, and avoiding getters/setters. The agenda involves a discussion of OOP concepts and a coding exercise on implementing LCD number display following the Object Calisthenics rules.
Coding Dojo Object Calisthenics (2016)
- 1. Object Calisthenics October 2016 PeterKofler, ‘Code Cop’ @codecopkofler www.code-cop.org Copyright Peter Kofler, licensed under CC-BY.
- 2. Peter Kofler • Ph.D.(Appl. Math.) • Professional Software Developer for 15+ years • “fanatic about code quality” • Freelance Code Mentor PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 3. I help developmentteams with PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY ● Professionalism ● Quality and Productivity ● Continuous Improvement
- 4. Mentoring PETER KOFLER, CODE-COP.ORGFANATIC ABOUT CODE QUALITY ● Pair Programming ● Programming Workshops ● Deliberate Practice, e.g. Coding Dojos
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- 6. Agenda ● Concepts of OO ● Encapsulation ● Couplingand Cohesion ● Coding Exercise “Object Calisthenics” PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 7. Discussion ● What is ObjectOrientation? ● What are its basic features? PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 8. OOP is basedon ● Abstraction ● Encapsulation ● Polymorphy ● Inheritance ● Coupling ● Cohesion PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 9. Abstraction ● “A class shouldcapture one and only one key abstraction.” ● Avoid Primitive Obsession. ● Single Responsibility Principle (SRP). ● Wrap All Primitives And Strings. (OC#3) ● First Class Collections. (OC#4) ● Keep All Entities Small. (OC#7) PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 10. Encapsulation ● “Objects are definedby what they do, not what they contain.“ ● All data should be hidden within its class. ● Tell, Don't Ask. ● e.g. ● All fields must be private. ● No Getters/Setters/Properties. (OC#9) PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 11. Polymorphy ● Avoid switch statements(Type Code). ● “Explicit case on the type of an object (instanceof) is usually an error.” ● Open Closed Principle (OCP). ● e.g. ● Avoid switch statements. ● Don’t Use The else Keyword. (OC#2) PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 12. Inheritance ● „Inheritance should onlybe used to model a specialization hierarchy.“ ● “IS A ...“ vs. „HAS A ...“ means the subclass “IS exactly the same AS …” ● Inheritance hierarchies should be shallow. (2-3) ● See Liskov Substitution Principle (LSP). PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
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- 14. Low Coupling ● “Minimize thenumber of classes with which another class collaborates.“ ● “Minimize the number of messages sent between a class and its collaborator.“ ● Law of Demeter (“Only talk to friends”). ● See Interface Segregation Principle (ISP). ● e.g. ● One Dot (dereference) Per Line. (OC#5) PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 15. High Cohesion ● “Most ofthe methods defined on a class should be using most of the data members most of the time.“ ● Related data and behaviour in one place. ● e.g. ● Don’t Abbreviate (long names). (OC#6) ● Keep All Entities Small. (OC#7) ● Max Two Instance Variables. (OC#8) PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 16. Jeff Bay's ObjectCalisthenics 1. Only One Level Of Indentation Per Method. 2. Don’t Use The else Keyword. 3. Wrap All Primitives And Strings. 4. First Class Collections. 5. One Dot/Arrow (dereference) Per Line. 6. Don’t Abbreviate (long names). 7. Keep All Entities Small. (50 LoC per class) 8. Not More Than Two Instance Variables. 9. No Getters/Setters/Properties. PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 17. Try it yourself PETERKOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 18. Coding Dojo Mindset ● Safeplace outside work ● We are here to learn ● Need to slow down ● Focus on doing it right ● Collaborative Game PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 19. Rules PETER KOFLER, CODE-COP.ORGFANATIC ABOUT CODE QUALITY
- 20. Pair Programming &TDD ● regular Pair Programming ● do not talk for too long ● do not interrupt the other ● no “keyboard hugging“ ● use TDD (or at least “sort of” TDD) ● write a test before you write code ● refactor mercilessly ● no debugger PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 21. LCD Numbers PETER KOFLER,CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 22. Assignment ● Create anLCD string representation of an integer value using a 4x7 grid of space, minus and pipe characters for each digit. ● Each digit is shown below (dot instead of space) .--......--..--......--..--..--..--..--. |..|...|...|...||..||...|......||..||..| |..|...|...|...||..||...|......||..||..| .........--..--..--..--..--......--..--. |..|...||......|...|...||..|...||..|...| |..|...||......|...|...||..|...||..|...| .--......--..--......--..--......--..--. ● Bar size should be adjustable. The default value is 2. PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 23. “Calisthenics” Constraint PETER KOFLER,CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 24. Jeff Bay's ObjectCalisthenics 1. Only One Level Of Indentation Per Method. 2. Don’t Use The else Keyword. 3. Wrap All Primitives And Strings. 4. First Class Collections. 5. One Dot/Arrow (dereference) Per Line. 6. Don’t Abbreviate (long names). 7. Keep All Entities Small. (50 LoC per class) 8. Not More Than Two Instance Variables. 9. No Getters/Setters/Properties. PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 25. Prepare ● Find a pair. ● Choosea programming language. ● Get the Java project or create new one. ● Implement LCD Numbers. PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 26. Don't Focus on Gettingit Done. F0cus on Doing It Perfectly.
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- 28. Closing Circle ● What didyou learn today? ● What surprised you today? ● What will you do differently in the future? PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 29. Peter Kofler @codecopkofler www.code-cop.org PETER KOFLER,CODE-COP.ORG FANATIC ABOUT CODE QUALITY
- 30. CC Images ● Brucehttp://www.flickr.com/photos/sherpas428/4350620602/ ● pairing http://www.flickr.com/photos/dav/94735395/ ● agenda http://www.flickr.com/photos/24293932@N00/2752221871/ ● wants you http://www.flickr.com/photos/shutter/105497713/ ● city http://www.flickr.com/photos/42311564@N00/2411037726/ ● hands https://www.flickr.com/photos/ninahiironniemi/497993647/ ● dojo http://www.flickr.com/photos/49715404@N00/3267627038/ ● rule http://www.flickr.com/photos/phunk/4188827473 ● LCD https://www.flickr.com/photos/ta3/3275907319/ ● calisthenics https://www.flickr.com/photos/snickclunk/18522120656/ PETER KOFLER, CODE-COP.ORG FANATIC ABOUT CODE QUALITY