In polymorphism, the type of the variable, but not the type of the referenced object, determines which method is called.

Invoking a method on a subclass object via a superclass reference invokes the subclass functionality.

In polymorphism, an object of a superclass is not an object of any of its subclasses.

In polymorphism, an object of a subclass can be treated as an object of its superclass, enabling various interesting manipulations.

A program can create an array of superclass variables that refer to objects of many subclass types.

In polymorphism, a technique known as downcasting enables a program to invoke subclass methods that are not in the superclass.

In polymorphism, the is-a relationship applies only up the hierarchy from a subclass to its direct (and indirect) superclasses, and not down the hierarchy.