In a Java interface, is there a way to return an enum nested in a generic type?

Question

I'm looking for a way to return an Enum type nested in a Generic class. Here's what I mean:

public interface MapperClass<E, D> {

    D entityToDto(E entity);

    default List<D> entitiesToDto(List<E> entities) {
        return entities.stream()
                .map(this::entityToDto)
                .collect(Collectors.toList());
    }

    D.Enum mapString(String str);
}

In other words, my method mapString() should return an enum that is nested in the generic type D, is there a way to accomplish this in Java?

Answer 1

May be something like this:

public interface MapperClass<E extends Enum<Test.TestEnum>, D extends Test> {
    E mapString(String a);
    ..
}

Your Test Class:

public class Test {
    ..
    enum TestEnum{
        A,B,C; //for demonstration purpose
    }
  ..
}

Interface implementation example :

 MapperClass<Enum<Test.TestEnum>, Test> a=new  MapperClass<Enum<Test.TestEnum>, Test>() {
       ..
            @Override
            public Enum<Test.TestEnum> mapString(String a) {
                return Test411.A; 
            }
       ..
     }