Java: Wildcard type vs plain type

Question

A method eat() uses a parameter of type Food, while Food is a generic class:

class Food<T> {
    T type; 
    ...
}


class Human {
    public void eat Food(Food food) {
        // eat, eat, and eat, however it has nothing to do with T
    }
}

The question is, should I declare Food<?> instead of Food in eat's parameter? Are there any difference while the method eat doesn't care and use anything related with T?

Are generics really what you want here? Maybe try mkaing `Food` an interface, and use specific implementations if needed required. — Alex M, Sep 03 '18 at 08:43
Maybe you currently don't care that `T` could be any type of object. All you need is the toString() or something like that. But it could be useful to establish a base FoodType (Interface). So, if you later do need assumptions that should be common to every FoodType, then those will be guaranteed to be in place. — Patrick Parker, Sep 03 '18 at 08:50
The difference is that with `Food food` you can assign anything you like to `food.type`, e.g. a `String`, an `Integer`, a `Frobnitz`. If the value you pass the method as a parameter is, say a `Food`, that will (may) lead to a problem later (specifically, a `ClassCastException`). `Food> food` prevents this. Raw types: stay away. — Andy Turner, Sep 03 '18 at 08:51

score 0 · Answer 1 · answered Sep 03 '18 at 08:43

If you use just Food, then you're using a raw type. The compiler will issue a warning, since it loses any information and cannot do any type checks on subsequent uses of this type. So if you don't care about T inside the method, use Food<?> and let the compiler know about this fact.

Java: Wildcard type vs plain type

1 Answers1