Extreme Programming

Extreme Programming XP EXTREME PROGRAMMING Joint Advanced Student School (JASS)

Outline • What is XP? • Motivation • XP values • XP features • Rules and practices of XP • Example: Pair Programming • Conclusion • Experiment: Pair Drawing

What is XP? A system of practices that a community of software developers is evolving to address the problems of quickly delivering quality software, and then evolving it to meet changing business needs.

Extreme?

Common problems of software development: Schedule slips Business misunderstood Defect rate Management Motivation of developers Motivation XP solutions: • Short iterations, fast delivery • Whole team • Test driven development • Shared understanding • Humanity and productivity • Why do we need XP?

Motivation • Economics of Software Development Classic approach XP approach Cost of change Cost of change Requirements Analysis Design Implementation Testing Production Time Time Iterations

XP values Courage Communication Simplicity Feedback

XP features • XP is the most suitable for: • Small and medium size projects • New technologies • Projects with unclear requirements • Risky projects • XP improves skills by cross training • No more than 20 developers in a team • Using of XP in life-critical projects is questionable

Rules and practices Planning Designing Extreme Programming Coding Testing http://www.extremeprogramming.org

The planning game Business Desired features User stories Business Determine Project Velocity Estimate stories Development Development Prioritize Business Plan overall release Plan next iteration Business Development

Designing Simple program to explore potential solutions. Address only one problem at a time. The metaphor is a simple meaningful description of how the program works. The metaphor is a simple meaningful description of how the program works. • Simplicity • System metaphor • Spike solution • Refactoring Always use the simplest possible design that gets the job done. K.I.S.S. - Keep It Short and Simple Ongoing redesign of software to improve responsiveness to change

Coding The customer is always available. • On-site customer • Collective ownership • Pair programming • Coding standards • No overtime Code must be written to agreed standards. Java Naming Conventions Classes: Node, Reader, AssignableVariable Variables: node, reader, variable Member variables: m_imageSource, m_reader; Methods: append(), getSource(), deleteIfEmpty() Mutator Methods: setToyOwner(String ownerName) Any developer can change any line of code to add functionality, fix bugs, or refactor. 40-Hour Work Week Programmers go home on time.

Testing • Extreme testing? • Code test first • Unit tests • Acceptance tests Testcase is the specification

Pair Programming Example

Example What is our task? How do we calculate that? And how? Nice, so lets start with creating a 'customer' class. We have to calculate the fee for the rented DVDs. The price depends on the number of days that you rent a DVD. Let me see... Our cards says, that regular movies are 2EUR for 2 days. After the third day it's 1.5EUR per day. Wait! Let us write a testcase for it...

Example public class CustomerTest extendsjunit.framework.TestCase { public CustomerTest(String name) { super(name); } }

Example The best thing is, that we write a testcase-method testRentingOneMovie, which checks the renting-fee for the movie. The framework looks for all methods that begin with 'test' and runs them. What's the first testcase? And how? And where do we put the testcode? Good, let's write down what we have so far. First we need a customer. And then we act like we have all the methods that we'd like to have. That's easy :) The simplest thing to start is renting one movie. For every method we write asserts to assure that it is working. Right. We rent a DVD for one day and the fee should be 2 EUR.

Example public class CustomerTest... public void testRentingOneMovie() { Customer customer = new Customer(); customer.rentMovie(1); assertTrue(customer.getTotalCharge() == 2); } }

Example Ok. You want me to make this test running and forget everything else for the moment. That's also easy :) Exactly. What would you do, if you only had to implement this single test?

Example public class Customer { public void rentMovie(int daysRented) { } public int getTotalCharge() { return 2; } } How extreme... But good :) Test a bit, code a bit, test a bit more

Example How extreme... But good :) Test a bit, code a bit, test a bit more public class CustomerTest... public void testRentingTwoMovies() { Customer customer = new Customer(); customer.rentMovie(1); customer.rentMovie(2); assertEquals(4, customer.getTotalCharge()); } }

Example public class Customer { private int totalCharge = 0; public void rentMovie(int daysRented) { totalCharge += 2; } public int getTotalCharge() { return totalCharge; } }

Conclusion • Communicate intensively • Test a bit, code a bit, test a bit more • Keep the design simple • Refactor • Enjoy having a safety net when refactoring What you should take with you now

Have fun and thank you!

Experiment: Pair Drawing • How did you feel when you were drawing solo vs. in a pair? • Which of the drawings are more artistic / original? • Did you find yourself concentrating more or less during pairing? • Was it more fun to draw alone or in a pair? • What did you like and what didn’t you like about drawing alone or in a pair? http://industriallogic.com/games/pairdraw.html

Extreme Programming