• Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other Pie Elite all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Ron McLeod
  • Rob Spoor
  • Tim Cooke
  • Junilu Lacar
Sheriffs:
  • Henry Wong
  • Liutauras Vilda
  • Jeanne Boyarsky
Saloon Keepers:
  • Jesse Silverman
  • Tim Holloway
  • Stephan van Hulst
  • Tim Moores
  • Carey Brown
Bartenders:
  • Al Hobbs
  • Mikalai Zaikin
  • Piet Souris

Overriding doubt in K&B

 
Ranch Hand
Posts: 105
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hello ranchers,

In K&B Rules for overriding a method - page 102 last point

"The Overriding method can throw newer or fewer exceptions.
Bottom Line: an Overriding method does'nt have to declare any exceptions that it will never throw, regardless of what the overridden medhod declares."

If this is right, why should you get a compiler error with the following code?

page 104 Exam Watch

class Animal{
public void eat() throws Exception {
}
}

class Dog2 extends Animal {
public void eat(){ // No exceptions }
public static void main(String [] args) {
Animal a = new Dog2();
Dog2 d = new Dog2();
d.eat();
a.eat(); //compiler error- unreported exception
}
}

This code will not compile because of the Exception declared on the Animal eat() method. This happens even though, at runtime, the eat() method used would be the Dog version, which does not declare the exception.

Can anyone please explain. For be both look so contradicting.

Thank you
 
Ranch Hand
Posts: 7729
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Variable a is a reference to an Animal, so it is Animals eat() method which is being checked for exceptions by the compiler. Animals.eat() declares it throws Exception but you do not catch them or declare that your main method throws them.
 
Ranch Hand
Posts: 64
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
As Overriding is done at runtime by jvm.But compiler will see the refernce variable i.e Animal class & invoke public void eat() throws Exception{} but at that time compiler Notice that exception is not handle. So it is giving exception. Definately it will call Dog2 's eat if you follow overriding rules.
 
Siri Naray
Ranch Hand
Posts: 105
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
So what should I do for this code not to generate any compiler error? Just handle the exception?
 
Ranch Hand
Posts: 809
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Handle it by try/catch or put it in throws clause in main method.

Naseem
 
You showed up just in time for the waffles! And this tiny ad:
Building a Better World in your Backyard by Paul Wheaton and Shawn Klassen-Koop
https://coderanch.com/wiki/718759/books/Building-World-Backyard-Paul-Wheaton
reply
    Bookmark Topic Watch Topic
  • New Topic