What is the Role of casting in java program?

Answer 1

Casting an object to a child object is to make accessible fields, methods, etc that are found only in a child. For example.

ObjectA has field apples, and

ObjectB (which extends ObjectA) has field bananas, and

ObjectC (which also extends ObjectA) has field strawberries.

We created an instance of ObjectB which is of type ObjectA , Represented like this:

"ObjectA my_instance = new ObjectB();" //Since ObjectB extends ObjectA, we can make my_instance of type ObjectA

We can access apples:

"my_instance.apples"

Since my_instance is of the type ObjectA, any field from ObjectA is accessible such as apples, HOWEVER ObjectA does not contain the field bananas, so how do we access bananas? (And we can do it since we created an INSTANCE of ObjectB not ObjectA).

We do it by casting like this:

"((ObjectB) my_instance).bananas" <<We can now access apples AND bananas

This is what casting is used for.