Facilitating the Spread of Knowledge and Innovation in Professional Software Development

Write for InfoQ


Choose your language

InfoQ Homepage News Crap4J Seeks to Use Algorithms to Determine Code Quality

Crap4J Seeks to Use Algorithms to Determine Code Quality

This item in japanese

The goals of a new project, crap4j, are clear:

There is no fool-proof, 100% accurate and objective way to determine if a particular piece of code is crappy or not. However, our intuition backed by research and empirical evidence is that unnecessarily complex and convoluted code, written by someone else, is the code most likely to elicit the "This is crap!" response. If the person looking at the code is also responsible for maintaining it going forward, the response typically changes into "Oh crap!"

Expanding upon the initial reactions, a more precise measurement is needed. Crap4j provides a single number that combines complexity and test code coverage.

Given a Java method m, CRAP for m is calculated as follows:

CRAP(m) = comp(m)^2 * (1  cov(m)/100)^3 + comp(m)

Where comp(m) is the cyclomatic complexity of method m, and cov(m) is the test code coverage provided by automated tests (e.g. JUnit tests, not manual QA). Cyclomatic complexity is a well-known and widely used metric and itís calculated as one plus the number of unique decisions in the method. For code coverage we use basis path coverage.

Like any metric, this number needs to be used with caution and not blindly followed, but it does provide a starting point to facilitate change and a way to pinpoint places in the code that are in more need of updating than others.

Low CRAP numbers indicate code with relatively low change and maintenance risk because itís not too complex and/or itís well-protected by automated and repeatable tests. High CRAP numbers indicate code that ís risky to change because of a hazardous combination of high complexity and low, or no, automated test coverage.

Crap4j can be downloaded from, and is currently a plug-in for Eclipse. From more information, JUnitFactory has provided an introductory article.

Rate this Article