Downcasting

[Harikrishna Gorrepati]

Hi,

I have given the question in the comments..Please advice.

interface Universe{}
class India{}
class AP extends India implements Universe{}
class Hyderabad extends AP{}

public class P114_TypeCast18_Ask {
    
    public static void main(String args[]) {
	
	Universe universeRef = null;
	
	AP apRef = new AP();
	apRef = (Hyderabad)universeRef;	//What is the meaning if this line.. Are we downcasting from 
                                    //universeRef(referring to null) to Hyderabad and assigning it to AP ??
					                //Downcasting a null reference to some other object is not a problem ?? 
   }
}

[Ankit Garg]

Yes null value is downcasted to type Hyderabad and then automatically upcasted to AP. null value can be type casted to any type which is not a primitive...

[Rahul Saple]

Yes, we are explictly downcasting the reference (Universe) to Hyderabad and the compiler does the implicit Upcasting (since it is always error free) for us. Assigning a null value is never a problem. Only using(calling a method, accessing a field) a reference pointing to no object in particular(null) leads to an exception. Infact, a non-local reference variable when declared has its default value set to null.