Java ArrayList of ? extends Interface

Question

I have a group of classes that all implement a validation interface which has the method isValid(). I want to put a group of objects--all of different classes--

Answer 1

List myValidationObjects

Incorrect reading

"myValidationObjects is list of objects that extend Validation."

Correct reading

"myValidationObjects can be a list of any type that extends Validation. For example, it could be a List or a List."

Since there is no object you can legitimately add to both a List and a List, Java prevents you to call add on a variable of such type.

Your case is in fact the simpler one: you need the definite type List.