Java Generics: Wildcard capture misunderstanding

Question

Reading the Java online tutorial I haven\'t understand anything about wildcard capture. For example:

    import java.util.List;
    public class WildcardErro         


        

Answer 1

I guess your misunderstanding of the restriction comes from substitution of ? for any type, Object or something like that in your mind. But that assumption is not correct, ? in fact means unknown type. So in the following line

fooz.set(0, foo);

you're trying to assign the variable of some type to the variable of unknown type (since the function signature is like void set(int, ?)), which can never be possible, whatever the type of foo would be. In your case the type of foo is Object and you cannot assign it to a variable of some unknown type, which in fact may be Foo, Bar or any other.