是否可以让方法签名成为它实现的接口的子类型？

Question

Say I have an interface:

public interface IDto {
}

and a class that implements this interface:

public class UserProfileResponseDto implements IDto {
}

In another interface I have:

public interface ISortingController {
    public List<IDto> findAll();
}

In my concrete controller I have:

public List<UserProfileResponseDto> findAll();

but its telling me that it must be

public List<IDto> findAll();

Is there a way that would allow public List<UserProfileResponseDto> findAll(); as it feels like it should be allowed since UserProfileResponseDto implements IDto . The reason I ask this question is because I feel that it gives more verbosity the the controller class, which would make it easier to maintain and operate with.

Answer 1

You need to declare a type parameter in your ISortingController like this:

public interface ISortingController<D extends IDto> {
    public List<D> findAll();
}

and your controller implementation needs to say implements ISortingController< UserProfileResponseDto> .