Redundant generic parameters

Question

I have this two interfaces and classes:

public interface Identifiable {
    T getId();
}

public interface GenericRepository

        

Answer 1

It's not redundant from the standpoint of the GenericRepository class. When it has methods like T get(K id), it can't know which types of the id argument it can accept otherwise. You can write the following:

interface GenericRepository> {
    T get(Object id);
}

Now you don't have to write Long as a type parameter, but you lose the possibility to check if the get method is used properly at compile time. So the type variable serves a specific purpose.

And as for the field declaration, when you have a generic type, you have to specify all the type variables it uses. Of course, you could argue that it would be neat if the language could understand that one of the parameter values can be inferred from the other one, but it is debatable.