What is the difference between <? super T> and <? extends T> in Java generics?

Greetings, colleagues! I started learning Java generics and encountered wildcards. I read the documentation and watched videos, but I'm still confused about two constructs: `` and ``. I understand that `? extends T` means "some type that is a subtype of T", and `? super T` means "some type that is a supertype of T". But in practice, I keep getting compilation errors. For example, I have this code with List: ```java public class Test { public static void addNumbers(List list) { list.add(42); // This works } public static void readNumbers(List list) { Integer num = list.get(0); // This works list.add(42); // Compilation error! Why? } } ```