java:S6204 Suggestion of using .toList() in a List that is from the interface does not compile

Rules and Languages Report False-positive / False-negative...
1

Sonar is constantly asked to use .toList() in addition to .collect(Collectors.toList()) but in some cases this request is wrong as the solution simply won’t compile.

Here’s a small example:

public interface TestSonar {

}


@RequiredArgsConstructor
public class ReturnTestSonar {
    @Getter private final List<TestSonar> list;
    
    @RequiredArgsConstructor
    public static class TestSonarImpl implements TestSonar {
        @Getter private final Integer integer;
    }

}


public class SonarViolation {
        
    public List<TestSonar> teste(List<Integer> list) {
        return list.stream().map(TestSonarImpl::new).collect(Collectors.toList());
    }
    
    public ReturnTestSonar myList(List<Integer> list) {
        return new ReturnTestSonar(list.stream().map(TestSonarImpl::new).collect(Collectors.toList())); 
    }
}
4

Hello @Irineu_Ruiz, thanks for reaching out.

I assume you are getting the issues raised on the following lines:

return list.stream().map(TestSonarImpl::new).collect(Collectors.toList());

and

return new ReturnTestSonar(list.stream().map(TestSonarImpl::new).collect(Collectors.toList()));

Can you confirm it?

In these cases, the rule is valid and you should replace the .collect(Collectors.toList()); with .toList();. The compliant code will be the following:

return list.stream().map(TestSonarImpl::new).toList();

and

return new ReturnTestSonar(list.stream().map(TestSonarImpl::new).toList());

I hope this helps you, and in case I’m missing something don’t hesitate to let me know.

Cheers

6

Angelo,
Sorry for the delay in responding, but apparently I hadn’t been notified of your response.

So, the suggestion you gave does not compile, because then I would have to change the return of the method to be the TestSonarImpl instead of the interface TestSonar.