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exception in overridden

Rishi Wright
Ranch Hand

Joined: Jun 25, 2003
Posts: 46
Hi 'LL
I wanted to know why an overriding method cannot throw any checked exception other than the same excpetion or subclass of an exception thrown by the overrridden method??
why java made it necessary..
thank you
rishi
Anand R Kulkarni
Greenhorn

Joined: Aug 06, 2003
Posts: 4
Hi,
Greetings all. I give my thoughts on this:
Overriding is a form of polymorphism. We all know when we override a method,
the same method exists in its super class with probably different implementation.
Also, it is possible to cast subclass' object to superclass' and call superclass' methods.
Subclass is basically "a super class" with added functionalities.
So when we call superclass method ( typically overridden method), the sub class overridden method
at least 'should match' its superclass method.
The subclass method should 'at least' be same as its superclass
with respect to access and also exceptions thrown if any.
Again, if subclass throws same or more specific ( i.e. subclass of exception), it is possible to cast to its superclass.
but not vice versa. So the restictions for exceptions and also for access.
i.e Overridden method is 'at least' have access of its super class method or more 'access' but not less.
Pardon me if I confused you more!

Regards,
Anand Kulkarni
Alton Hernandez
Ranch Hand

Joined: May 30, 2003
Posts: 443
Hi Rishi,
This is what the book "The Java Programming Language, 3rd Edition" book says:

..code written to deal with the original method declaration will not be prepared to catch any additional checked exceptions and so no such exceptions are allowed to be thrown.

Consider the following code. If it is allowed for overriding method to throw more checked exception, then line 2 will fail.
 
Consider Paul's rocket mass heater.
 
subject: exception in overridden