Incorrect Code Smell on functional interface usage (S4276)

SonarQube (Version 8.0 (build 29455) ) reports code smell with “Functional Interfaces should be as specialised as possible” when I use Function<T, Integer> instead of ToIntFunction<T>. But the specialised implementation is not allowed by the compiler. I’m using it inside Collectors.toMap.

SO Link with code sample

Hello Master Ping Po,

First, let me welcome you in this forum, and thank you for your feedback.

Indeed, in such case, rule S4276 is raising a False Positive (FP), and the rule should not recommend to use the more specialized interface. I created the following ticket to improve the rule: SONARJAVA-3265