Can you please explain why it is possible to do: import java.util.ArrayList; import java.util.List; public class Covariance {
Class B extends class A. I have a list of B (List<B> list1), but for some operations I need only class A fields, but List<A> list2 = list1 doesn\'t work. H开发者_如何学Cow can this problem
The code is a little weird, so bear with me (keep in mind this scenario did come up in production code).
In Java I can specify generic with wildcard \"?\". It is possible to create a map like this one: Map<String, ?>.
I have a function which returns a list of products and a page which displays then, but when I try to load the list on the page, I get a cryptic error:
I am pretty new to Scala and advanced programming languages. I try to solve the following problem. I have got:
I have a List of objects, which are of my type QuoteHeader and I want to pass this list as a list of objects to a method which is able to accept a List<object>.
I got the classic Shape hierarchy example... struct Shape { // abstract type Shape (int x, int y); int x;
I have something link this: public abstract class Wrapper<T, TWrapped>: where TWrapped : Wrapper<T, TWrapped>
I would like a Covariant collection whose items can be retrieved by index.IEnumerable is the only .net collection that I\'m aware of that is Covariant, but it does not have this index support.
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