Enthuware

Hi,
I'm a little bit angry with multi casting !!
So, if I understand the order is important (B)(I)b is not the same as (I)(B)b ?
Thnks

To understand multiple casts, just break them up, and check the validity of each individual cast. For example, (B)(I)b can be broken up like this:

I tempI = (I)b;
B tempB = (B) tempI;

and (I)(B)b can be broken up as:

B tempB = (B)b;
I tempI = (I)b;

Now, you can easily figure out which casts are valid and which are not and whether order is important or not.

HTH,
Paul.

Ok I'll try to keep this method in my brain !!
Thnks

The explanation says: "A reference of type I can be cast to any class at compile time."
Why is it so? Why compiler can't figure out which class not is-a I?

Because an interface can be implemented by any class. So at run time the reference may point to an instance of a sub-class that extends a class and also implements the interface. That is why even though the compiler knows that a particular class does not implement I, it cannot reject the cast. A subclass of that class may implement the interface.

admin wrote:A subclass of that class may implement the interface.

That's the point I forgot, thank you!

Hi,

When i executed the below code, i get "class cast exception that B cannot be cast to I". b can be casted to I and I can be casted to B and since B is a A, it should run without exception. So why am I getting this error.

Can you please help me understand, why is the compiler throwing class cast exception.

interface I {}
public class A implements I1
{
public static void main(String[] args)
{
A a=new A();
B b=new B();
a=(B)(I)b;

}
}

class B extends A { }

class C extends B { }

Sorry, got it. no problem.

How do i check the validity of each cast ? What criteria or questions do i have to ask in order to decide if a cast is right or not ? Is it always the Is-A relationship ?
i.e:
a = (B)(I)b;

Where will i start and how will i proceed ?

horst1a wrote:How do i check the validity of each cast ? What criteria or questions do i have to ask in order to decide if a cast is right or not ? Is it always the Is-A relationship ?
i.e:
a = (B)(I)b;

Where will i start and how will i proceed ?

Which book are you following?
If you are not following any book, try this article: https://howtoprogramwithjava.com/java-cast/