CODEWITHSUNDEEP
javaoopinheritancepolymorphism
yasgur99
yasgur99

Reputation: 858

Return ? extends Type

I want to have a method signature that looks as such:

public <? extends IDto> convertToResponseDto();

I came up with this from a valid signature that looks like:

public List<? extends IDto> convertToResponseDto();

As it turns out Type <? extends IDto> is not a valid return type. I feel like the intention of what I am trying to return is quite clear, but not sure what the correct syntax is

EDIT

This question was answered by @ErwinBolwidt, but gives a new problem in a use case. I have a case where I am using generics: 

protected final <E extends IDto> E findOneInternal(final Long id) {
        return getService().findOne(id).convertToResponseDto();
}

In this case, convertToResponseDto() returns IDto, and not the concrete class, as its not known at this pint because it gets the service of type T

Upvotes: 0

Views: 106

Answers (2)

Erwin Bolwidt
Erwin Bolwidt

Reputation: 31299

You can override an interface method or superclass method with a more specific subtype as the return type. Say your superclass says 

public IDto convertToDTO()

Then your subclass can say 

public MySpecificDTO convertToDTO()

That's implied by the Java language and doesn't need any generics.

Upvotes: 2

Julian Cardona
Julian Cardona

Reputation: 1

You can define a generic type

public <T extends IDto> T convertToResponseDto();

Upvotes: 0

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