Capturing wildcards in Java generics

Question

From this Oracle Java tutorial:

The WildcardError example produces a capture error when compiled:

public class WildcardE         


        

Answer 1

List<?> does mean list of object of unknown type, it's not the same as List<Object>.

Because we don't know the type of elements in the list result of i.get(0) is considered by Java as Object, and you cannot add Object to List<?>. In case as your Java could be smarter, but in more complex code with <?> wildcards it's easy to make it no type safe.