Limit generic type in subinterface in Java

问题

Say I have this interface structure:

public interface ItemRequestConverter<IR extends ItemRequest> {
    Target convert(IR request);
}

public interface CreateItemRequestConverter<CIR extends CreateItemRequest>
    extends ItemRequestConverter<ItemRequest> {
}

public class CreatePartRequestConverter implements CreateItemRequestConverter<CreatePartRequest> {
    @Override
    public Target convert(CreatePartRequest request) {
        ...
    }
}

Now I wondering whether this is possible at all. I doubt that. When I create CreatePartRequestConverter the signature of the overridden method is the super type ItemRequest. This is not desired.

回答1:

I think your CreateItemRequestConverter class signature should be like this :

interface CreateItemRequestConverter<CIR extends CreateItemRequest>
        extends ItemRequestConverter<CIR> {

}

Test :

interface ItemRequestConverter<IR extends ItemRequest> {
    Target convert(IR request);
}

interface CreateItemRequestConverter<CIR extends CreateItemRequest>
        extends ItemRequestConverter<CIR> {

}

class CreatePartRequestConverter implements CreateItemRequestConverter<CreatePartRequest> {
    @Override
    public Target convert(CreatePartRequest request) {
        return null;
    }
}

class ItemRequest {
}

class CreateItemRequest extends ItemRequest {
}

class CreatePartRequest extends CreateItemRequest {
}

class Target {
}

回答2:

So you want to make the overridden method accept a generic type that extends ItemRequest? You'll want to use a generic method, e.g:

<T extends ItemRequest> Target convert(T request);

来源：https://stackoverflow.com/questions/21457226/limit-generic-type-in-subinterface-in-java

标签

java

generics

interface