Feature Request: Recipe to Extract Magic Numbers to Type-and-Value-Named Constants per Class

[boraciner]

Hi team,
In order to fix "Magic numbers should not be usedjava:S109" problems in my code.
I’d love to see a new recipe that detects all magic numbers scattered throughout a codebase and, for each unique magic number in a class, introduces a constant at the top of that class named using the pattern TYPE_VALUE (e.g., INT10 for 10, DOUBLE23_5 for 23.5). The recipe would then replace all usages of that magic number within the class with the generated constant.

Desired behavior:

For every integer/double/float/etc. literal not already assigned to a constant, automatically declare a private static final constant at the top of the class, following the TYPE_VALUE (or similar) naming convention.
Replace each magic number occurrence in the class with the appropriate constant.
Type and value should be part of the constant name (e.g., INT42, DOUBLE3_14), to avoid collisions and increase readability.
Support commonly used primitive types (int, double, float, long, etc.).
Motivation:

Prevents code duplication and improves maintainability.
Enables fully automated removal of magic numbers, even in large legacy projects.
This would be a huge help for modernizing legacy codebases with large numbers of magic numbers across many classes.

Thank you very much for considering this enhancement!

[timtebeek]

hi! Thanks for the suggestion; indeed could be doable as a recipe, but it's tough to decide when extracting a constant would lead to a readability improvement. Consider for instance the case list.get(0); I'd think it would hurt readability to turn that into list.get(INT0). That then quickly means the recipe can't extract all literals as proposed, meaning we'd need some heuristics that make things more complicated & opinionated. Do you see a clear way forward that would always improve readability? Perhaps starting at a small scale?

[knutwannheden]

I am not a fan of this warning either, but note that -1, 0, and 1 are not considered magic: https://sonarsource.atlassian.net/browse/RSPEC-109

We could still provide the recipe for users that have this SonarQube rule enabled, maybe?

[boraciner]

I implemented a recipe and today I'm going to create a pull request, please check that out. I will update this topic

[boraciner]

• Feature Request: Recipe to Extract Magic Numbers to Type-and-Value-Named Constants per Class #769