Polymorphism

• Polymorphism means "many forms."
• A reference variable is always of a single, unchangeable type, but it can refer to a subtype object.
• A single object can be referred to by reference variables of many different types —as long as they are the same type or a supertype of the object.
• The reference variable's type (not the object's type), determines which methods can be called!
• Polymorphic method invocations apply only to overridden instance methods.