Using Method Cast instead of Lambda on List with Objects

Question

I am working on fixing some Sonar - Codesmells in my project at the moment. Sonar is pointing me at this method:

    protected List<Long> rolesIdsFromPortalSpecificAuthorizations(final List<PortalSpecificAuthorization> portalSpecificAuthorizations) {
             return portalSpecificAuthorizations.stream().map(portalSpecificAuthorization -> portalSpecificAuthorization.getId()).collect(Collectors.toList());
}

It says:

Replace this lambda with a method reference.

The PortalSpecificAuthorization is an object from my own coding. I was not able to find an easy-to-use solution for this case with Method casts.
What is the correct usage in this case?

Answer 1

Sonar wants a Method Reference instead of the lambda.

Replace this part:

portalSpecificAuthorization -> portalSpecificAuthorization.getId()

with this

PortalSpecificAuthorization::getId

More about Method References: https://www.javatpoint.com/java-8-method-reference

---

Full Code:

protected List<Long> rolesIdsFromPortalSpecificAuthorizations(final List<PortalSpecificAuthorization> portalSpecificAuthorizations) {
    return portalSpecificAuthorizations.stream()
              .map(PortalSpecificAuthorization::getId)
              .collect(Collectors.toList());
}