EXtreme Programming (XP) is a lightweight, efficient, low-risk, flexible, predictable, scientific, and fun way to develop a software.

EXtreme Programming (XP) was conceived and developed to address the specific needs of software development by small teams in the face of vague and changing requirements.

Extreme Programming is one of the Agile software development methodologies. It provides values and principles to guide the team behavior. The team is expected to self-organize. Extreme Programming provides specific core practices where −

• Each practice is simple and self-complete.

• Combination of practices produces more complex and emergent behavior.

Embrace Change

A key assumption of Extreme Programming is that the cost of changing a program can be held mostly constant over time.

This can be achieved with −

• Emphasis on continuous feedback from the customer

• Short iterations

• Design and redesign

• Coding and testing frequently

• Eliminating defects early, thus reducing costs

• Keeping the customer involved throughout the development

• Delivering working product to the customer.

Extreme Programming in a Nutshell

• Writing unit tests before programming and keeping all of the tests running at all times. The unit tests are automated and eliminates defects early, thus reducing the costs.

• Starting with a simple design just enough to code the features at hand and redesigning when required.

• Programming in pairs (called pair programming), with two programmers at one screen, taking turns to use the keyboard. While one of them is at the keyboard, the other constantly reviews and provides inputs.

• Integrating and testing the whole system several times a day.

• Putting a minimal working system into the production quickly and upgrading it whenever required.

• Keeping the customer involved all the time and obtaining constant feedback.

Iterating facilitates the accommodating changes as the software evolves with the changing requirements.

Why is it called “Extreme?”

Extreme Programming takes the effective principles and practices to extreme levels.

• Code reviews are effective as the code is reviewed all the time.

• Testing is effective as there is continuous regression and testing.

• Design is effective as everybody needs to do refactoring daily.

• Integration testing is important as integrate and test several times a day.

• Short iterations are effective as the planning game for release planning and iteration planning.