Polymorphism, Upcasting, And Downcasting

1. Overview

Organize Polymorphism, Upcasting, and Downcasting. and then find usages and pitfalls each casting.

2. Description

Polymorphism Diagram

2.1 Polymorphism

The ability of an object to take on many forms. All methods in Java are virtual by default. so Any method can be overridden when used in inheritance unless that method is declared as final or static. When we cast object only the reference type of the object is changed but not the actual object type.

2.2 Upcasting

Derived class cast to Base class. Upcasting is safe and it does not fail.

Mammal m = new Cat();

2.2.1 pitfalls

• Object Slicing
• Losing where it is derived from.

2.3 Downcasting

Base class cast to a derived class. We need to check the instance of the object when we downcast the object using instanceof operator or we might get ClassCastException.

Cat c = (Cat) new Animal();

2.3.1 pitfalls

• Creating a phantom member.

4. Practices

https://github.com/demyank88/DesignPattern/tree/master/src/main/java/kr/co/practice/polymorphism