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The Art of Agile Development

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XP Concepts

As with any specialized field, XP has its own vocabulary. This vocabulary distills several important concepts into snappy descriptions. Any serious discussion of XP (and of agile in general) uses this vocabulary. Some of the most common ideas follow.




There are multiple ways of expressing the same concept in source code. Some are better than others. Refactoring is the process of changing the structure of code—rephrasing it—without changing its meaning or behavior. It’s used to improve code quality, to fight off software’s unavoidable entropy, and to ease adding new features.

Technical Debt

Imagine a customer rushing down the hallway to your desk. “It’s a bug!” she cries, out of breath. “We have to fix it now.” You can think of two solutions: the right way and the fast way. You just know she’ll watch over your shoulder until you fix it. So you choose the fast way, ignoring the little itchy feeling that you’re making the code a bit messier.

Technical debt is the total amount of less-than-perfect design and implementation decisions in your project. This includes quick and dirty hacks intended just to get something working right now! and design decisions that may no longer apply due to business changes. Technical debt can even come from development practices such as an unwieldy build process or incomplete test coverage. It lurks in gigantic methods filled with commented-out code and “TODO: not sure why this works” comments. These dark corners of ...

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