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Extreme Programming. Software engineering methodologies. A methodology is a formalized process or set of practices for creating software An early methodology was the waterfall model , so named because each stage flowed into the next, with no backing up to a previous stage - PowerPoint PPT Presentation
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Apr 19, 2023
Extreme Programming
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Software engineering methodologies
A methodology is a formalized process or set of practices for creating software
An early methodology was the waterfall model, so named because each stage flowed into the next, with no backing up to a previous stage
The stages were: Requirements Design Implementation Verification Maintenance
The waterfall model has never been regarded as a “good” model
Methodologies are subject to fads, and are frequently imposed on programmers by management
Some methodologies are bad—even ridiculously bad This doesn’t mean all methodologies are bad However, a single methodology doesn’t work for all cases
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Agile programming methodologies
There are (at least) two serious problems with the waterfall model: It assumes that there will be no unforeseen difficulties in the
software development It assumes that the customers know (and can specify) what
they want, in extreme detail Agile programming methodologies (of which there are
several) assume: Customers can best discover what software meets their needs
via frequent iterations Hence, communication between customers and developers is vital
Requirements will need to be revised, probably multiple times, during software development
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Extreme programming In this course we will draw on a number of ideas from one particular agile
methodology, Extreme Programming (XP) The basic idea of extreme programming is to take to an extreme each of
several known good practices “The first time I was asked to lead a team, I asked them to do a little bit of the
things I thought were sensible, like testing and reviews. The second time there was a lot more on the line. I thought, "Damn the torpedoes, at least this will make a good article," [and] asked the team to crank up all the knobs to 10 on the things I thought were essential and leave out everything else.” — Kent Beck
For example, it is well known that software should be tested frequently during development
Extreme programming advocates testing code literally every few minutes, after every minor change
Extreme programming works best for relatively small projects with a small number of good programmers
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XP values Communication
Use simple designs and common metaphors, talk continuously with your programmers and customers
Simplicity Follow the KISS principle (“Keep It Simple, Stupid!”)
Feedback From the system: Unit tests From the customer: Acceptance tests From the team: Estimate the time to implement new requirements
Courage Code for today, not tomorrow Refactor as appropriate Be willing to throw code away
Respect Trust your team members not to submit nonworking code
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XP practices
Fine scale feedback Pair Programming Planning Game Test Driven Development Whole Team
Continuous process Continuous Integration Design Improvement Small Releases
Shared understanding Coding Standards Collective Code
Ownership Simple Design System Metaphor
Programmer welfare Sustainable Pace
Source: http://en.wikipedia.org/wiki/Extreme_programming
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Pair programming is...
TWO programmers working side-by-side, collaborating on the same design,
algorithm, code or test. One programmer, the driver, has control of the
keyboard/mouse and actively implements the program. The other programmer,
the observer, continuously observes the work of the driver to identify tactical
(syntactic, spelling, etc.) defects and also thinks strategically about the
direction of the work. On demand, the two programmers can brainstorm any
challenging problem. Because the two programmers periodically switch roles,
they work together as equals to develop software.
--Laurie Williams
North Carolina State University Computer Science Source: http://www.pairprogramming.com/
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Pair programming in this course
One purpose of the Friday lab sections is to get you started pair programming on each project
After lab, you should work together with your partner as closely as possible
I know this may not be easy for some of you At least trade email addresses, and work together that way Instant messaging is often better If you have programming problems, go first to your partner for help
Reading assignment: All I Really Need To Know About Pair Programming I Learned In Kindergarten, by Laurie Williams and Robert Kessler (PDF)
The URL is too long to post here, but it’s on the class web page (or you can just Google for it)
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Test-Driven Development (TDD) TDD is a technique in which you write the tests before you
write the code you want to test This seems backward, but it really does work better:
When tests are written first, you have a clearer idea what to do when you write the methods
Because the tests are written first, the code is necessarily written to be testable
Writing tests first encourages you to write simpler, single-purpose methods
Because the methods will be called from more than one environment (the “real” one, plus your test class), they tend to be more independent of the environment
To do TDD, it must be easy to create and run tests JUnit is a framework that makes this much easier to do
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Continuous integration
Unit testing is testing a single, more-or-less independent part of a program in isolation
Integration testing is testing the complete program with all its parts, to make certain they all work together
Continuous integration is performing integration tests frequently (usually daily) Continuous integration is more important on larger projects For class projects, last-minute integration is still a bad idea
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Coding standards
Coding standards make it simpler for your teammates (or yourself, weeks later) to read your code
Java has some very well defined conventions you should learn Some conventions are strictly mechanical, such as formatting
(spacing and indentation) Eclipse can, upon request, correct your formatting for you
Some conventions require human intelligence Use meaningful names, with the correct part of speech Use adequate comments, written for the correct audience Prefer clearly written code to “clever” code
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Simple design
“Do the simplest thing that can possibly work” Complexity to achieve program efficiency is almost always a very bad
investment Complexity to support future features is seldom a good idea
Program for the features you need today, not the ones you think you will want tomorrow
With good unit tests, you can easily refactor (“revise”) your code to do additional tests
YAGNI -- “You ain’t gonna need it”
Follow the DRY principle: “Don’t repeat yourself” Don’t have multiple copies of identical (or very similar) code Don’t have redundant copies of information
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XP in this course Do pair programming in labs, and work as closely as possible
with your partner outside labs Use TDD (test-driven development) as much as possible
However, this really has to wait until you learn about methods and about JUnit
Stay in touch with your partner, and integrate your code as frequently as feasible
Follow the defined coding standards, including those for documentation
Keep your code as simple as possible You and your partner should turn in one copy of your program,
with both names on it
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What I expect of you Work as closely as you can with your partner
I realize this isn’t always easy Don’t just “contribute” your share of the code—also review your partner’s
code, checking for problems It’s okay to criticize your partner’s code; it’s not okay to criticize your partner Don’t take suggestions/criticisms/comments personally—any code can be
improved You can use all the Java you know, if your partner also understands it
If I haven’t covered something in class (or even if I have, but your partner doesn’t know it), it’s your job to explain it to your partner
If you don’t understand something in your partner’s code, ask them to explain it to you
Don’t: Depend on your partner to do it all Take off and do it all yourself
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The End
“All methodologies are based on fear.” --Kent Beck
“If we asked the customers what they wanted, it would be devastating for the project.” --Team lead on a project that shall remain nameless
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