Department of Computer Science, University of Sheffield

1. eXtreme Programming - Practices Dr. Marian Gheorghe Department of Computer Science, University of Sheffield

2. Plan • Example • Practices • Conclusions Department of Computer Science, University of Sheffield

3. Example: Customer/order subsystem Enter customer details (name, reference, address, phone, email); validate; edit Enter orders by customer (customer reference, order reference, order details, delivery date, invoice reference); validate; edit Department of Computer Science, University of Sheffield

4. Story cards • Story name: Enter and validate customer details • Task description: enter customer details and validate (ref. unique, name alphanumeric, phone numeric, address non-empty); if valid record then store it otherwise re-enter it. • Initiating event: a request made through choosing a menu option Department of Computer Science, University of Sheffield

5. Story card cont’d Memory context: customer records exist and will be updated Observable result: confirmation of success or prompting an error otherwise Related stories: Edit a customer details Notes: Mandatory Risk factor: 1(low) / Change factor: 1 (low) Department of Computer Science, University of Sheffield

6. Story card cont’d Functional tests Customer with a new reference, arbitrary data but alphanumeric name, non-empty address, numeric phone Customer with an existing reference Customer with either non-alphanumeric name or empty address or non-numeric phone Customer with empty fields (name, reference etc) Department of Computer Science, University of Sheffield

7. More story cards: 2. Edit customer details (validation included) 3. Enter and validate orders by customer 4. Edit orders (validation included) Department of Computer Science, University of Sheffield

8. The twelve sacred tenets of XP • Test first programming • Functional test sets; from story cards • Unit test sets (white-box: branch/condition/statement coverage) • Non-functional requirements tested Department of Computer Science, University of Sheffield

9. To get used to testing continuously – Run unit tests every time a new method/function has been created Run functional testing every time a new class, or set of functions implementing a story card Department of Computer Science, University of Sheffield

10. 2. Pair programming Any work involving code is done in pairs: two people – one computer Department of Computer Science, University of Sheffield

11. 3. On site customer: N/a 4. The planning game Story cards + cost estimations (how long it takes, how many people involved) Story cards discussed with the client Test sets associated with will help to understand some tricky conditions/new aspects; ask the client Department of Computer Science, University of Sheffield

12. 5. System metaphor A read.me file with the file structure of the project + a short description of the components An X-machine model of the system/subsystem Department of Computer Science, University of Sheffield

13. X-machine specification customer_proc end_customer pick_up_customer order_proc exit end_customer end_order Department of Computer Science, University of Sheffield

14. X-machine model State based model (states in green); with an initial state Transitions labeled by function names The model may contain functions which themselves will become X-machines (blue ones) Hierarchical model Department of Computer Science, University of Sheffield

15. customer_proc: search&display edit_customer change_customer click_customer enter_customer enter_detail error end_customer success validate_data Department of Computer Science, University of Sheffield Department of Computer Science, University of Sheffield

16. Function component Takes an input (click a button, enter some data) and a memory value then produces an output and updates the memory side. Formally: func_comp:: Input x Memory -> Output x Memory Department of Computer Science, University of Sheffield

17. Function components (examples) click_customer:: customer_btn x λ -> λ x customer_sel enter_customer:: enter_btn x customer_sel -> λ x customer_sel enter_detail:: data x customer_sel -> data_echoed x data where data =(name, reference,address,phone,email) Department of Computer Science, University of Sheffield

18. 6. Small, frequent releases Releases are not prototypes A release implement a couple of stories A release is thoroughly tested Releases are related to Department of Computer Science, University of Sheffield

19. 7. Continuous integration Write small units and test them (unit testing) Integrate into the system and test it functionally (test first programming) Suggestion: one pair be responsible for integrating components into an operational system Department of Computer Science, University of Sheffield

20. 8. Keep your code as SIMPLE as possible If it’s not so simple then… Department of Computer Science, University of Sheffield

21. 9. Refactoring • Restructuring the code without changing its functionality • Its main use is to simplify the code (Fowler) • -moving methods used in several classes in a new one • renaming classes, methods, functions • simplify conditional expressions; reorganise data Department of Computer Science, University of Sheffield

22. Refactoring (cont’d) Refactoring the test sets accordingly Changes into code require test sets changes as source code and test sets are the two main deliverables Department of Computer Science, University of Sheffield

23. 10. Code standards Should follow consistent class/method naming conventions Study coding standards before starting programming; decide upon a set of rules; show it to your manager Similar conventions should apply for test sets, story cards, metaphor Department of Computer Science, University of Sheffield

24. 11. Collective code ownership Coding standards help in using the same programming style Changes might be done by everyone in the team Suggestion: keep commenting your code with name, date and what has been changed; provide a change notification form Changes in the documents/story cards will be reflected only in notification forms and CVS variants. Department of Computer Science, University of Sheffield

25. 12. 48 hours/week => avg of 15hours/week Use your time adequately Department of Computer Science, University of Sheffield

26. Java coding standards(p.131-) • Each directory containing java files will contain a README file describing briefly these files • Each java source file will contain a single public class or interface • beginning comment: class name, author, date, version, changes description, changes history • a specified class structure Department of Computer Science, University of Sheffield

27. Java coding standards(cont’d) Each method should have a comment associated with Block comments vs single line comments One declaration per line + comment One stmt per line (simplicity) Layout for class decl, if, for, while, switch, try stmts Department of Computer Science, University of Sheffield

28. Coding standards Decide which standards you apply Apply them consistently (you’ll be marked on this basis!) The standards are there to help you produce simpler and easier to understand code Department of Computer Science, University of Sheffield

29. References K. Beck, “Extreme programming explained.” Addison-Wesley, 1999 K. Beck & M. Fowler, “Planning extreme programming.” Addison-Wesley, 2000 M. Holcombe, “Extreme programming for real: a disciplined, agile,approach to software engineering”, 2003 M. Holcombe & F. Ipate, “Correct systems: building a business process solution”, Springer, 1998. Department of Computer Science, University of Sheffield

30. Summary Are the 12 XP practices all applicable to SH projects? Simplify/apply partially some of them Enforce others Strengthen the testing side Department of Computer Science, University of Sheffield