Java - Polymorphism

a reference variable : a reference variable

- the only possible way to access an object is through _________

virtual methods

- virtual method invocation -An overridden method is invoked at run time, no matter what data type the reference is that was used in the source code at compile time.

a reference variable : refer

A reference variable can _____ to any object of its declared type or any subtype of its declared type.

a reference variable : a class or interface type

A reference variable can be declared as _______.

a reference variable : only one type

A reference variable can be of __________. Once declared, the type of a reference variable cannot be changed.

a reference variable : reassigned

The reference variable can be ________ to other objects provided that it is not declared final.

a reference variable : The type of the reference variable

________ would determine the methods that it can invoke on the object.

Polymorphism

_____________ is the ability of an object to take on many forms.

Java object that can pass more than one IS-A test

is considered to be polymorphic

most common use of polymorphism in OOP

occurs when a parent class reference is used to refer to a child class object.

Polymorphism Example

public interface Vegetarian{} public class Animal{} public class Deer extends Animal implements Vegetarian{} Now, the Deer class is considered to be polymorphic since this has multiple inheritance. Following are true for the above examples − A Deer IS-A Animal A Deer IS-A Vegetarian A Deer IS-A Deer A Deer IS-A Object When we apply the reference variable facts to a Deer object reference, the following declarations are legal -- Deer d = new Deer(); Animal a = d; Vegetarian v = d; Object o = d; All the reference variables d, a, v, o refer to the same Deer object in the heap.