What is the difference between Super thing = new Sub() and Sub thing = new Sub()?

Question

Super thing = new Sub();
Sub thing = new Sub();

What is the difference in terms of accessing thing and what I can do with it etc?

Answer 1

The difference is that the variabele Super thing can be reassigned to any other subclass that implements Super, whereas Sub thing of course can only be assigned to another Sub class.

That said, assigning new Sub() to Super thing uses polymorphism and overriding, of which you can find a good tutorial here and here. You can only call the methods defined in the class Super. If these methods are overridden (read: redefined) in one of the subclasses, polymorphism will make sure the overridden method is called, instead of the method in the class Super.