What's the difference between declaring the list as List<String> newList and ArrayList<String> newList = ...?

Hey, Yani! List is an Interface which has parameters and methods in it that classes have to implement in order to implement the interface. ArrayList is a class that implements the List interface. You should not be able to insatiate a new List<E>() because it is only an interface and not a fully developed class; however, you could declare a variable as a List<E> and then instantiate it as an new ArrayList<E>(). This is an example of polymorphism. There's a good article explaining what polymorphism is and its benefits and limitations here: http://www.artima.com/objectsandjava/webuscript/PolymorphismInterfaces1.html.

Does that help? If not, I can try to explain a little further. :)