Reference Variable Casting

[ragi singh]

Hi I have the following piece of code

class test2{
	
}
class test3 extends test2{
	
}
public class Test1{

	public static void main(String[] args){
		
		test3 t3=new test3();
		test3 t4= (test3) new test2();                           ///Line 1
		
	}
	
	public static void writer1(test3 t){
		
		System.out.println("Using the instance " + t);
	}
	
}

 

When i run the code i get the following exception :- Class cast exception at line Line 1 . My question is , Java allows downcasting then why is my code failing to compile ?

[Abimaran Kugathasan]

ragi singh wrote:
My question is , Java allows downcasting then why is my code failing to compile ?

You have misunderstood the down casting. Clue: Down casting for reference variable, not to objects. If you allowed to cast object, then what will be the real logic? You can't cast a object to any other object!

[Minhaj Mehmood]

Think about the relationships in real life, such as: A child can become parent, but a parent cannot become child again

Test2 is parent and you're forcing it to become child.


Hope this helps

Minhaj

[ragi singh]

that is to say we cannot downcast objects ?

[Abimaran Kugathasan]

ragi singh wrote:that is to say we cannot downcast objects ?

You can't cast a object! You can make sub class objects with super class reference and make a down cast it to refer with sub class reference again.

[ragi singh]

ok i got it now thank you .

[Abimaran Kugathasan]

You are Welcome. If we are allowed to cast a object into another, then there is no point of talking polymorphism and other stuff in Java! I think, now you got what does mean by down casting and up casting!