Overriden and Overriding Methods Declaration Conundrum.

[Abhijit Ghatnekar]

Hello All,


I'm very confused with the following piece of code that I have which fails to compile -

class Animal{
    public void eat() throws Exception {
        System.out.println("In Animal class");
    }
}

class Dog extends Animal{
    public void eat() {
        System.out.println("In Dog class");
    }
    public static void main(String[] args) {
        Animal a = new Dog();
        a.eat();
    }
}

This fails to compile due to the checked exception declaration in the superclass method eat()

I summarize the following rule of overriding concerning checked exceptions below

1) The overriding method MUST not throw any new or broader checked exceptions than those declared by the method in the superclass.

If I reason with this rule at the back of my mind, this code SHOULD compile. Furthermore, in the code the subclass object is assigned to a superclass reference which means in this case the subclass version of the eat method should execute successfully. Can anyone point me out of this dilemma?

Regds,
Abhijit.

[John Jai]

The method eat in the Animal class throws a Checked Exception. So it's necessary for you to handle it during compile time. The compiler will not know which object Animal reference will be pointing to.

[John Jai]

Adding to that the compiler will not complain if its a RuntimeException.

class Animal{ 
	public void eat() throws RuntimeException
	{ 
		System.out.println("In Animal class"); 
	} 
} 

public class Dog extends Animal{ 
	public void eat()
	{ 
		System.out.println("In Dog class"); 

	} 
	public static void main(String[] args)
	{ 
		Animal a = new Dog(); 
		a.eat(); 
	} 
} 

[Campbell Ritchie]

The fact that the Exception is unchecked does not make it better design. It simply means you can confuse the compiler.

[John Jai]

Campbell Ritchie wrote:The fact that the Exception is unchecked does not make it better design. It simply means you can confuse the compiler.

You are right... I just want to mention that the compiler error was due to the Checked Exception and not based on the overriding concept.

[Campbell Ritchie]

I could have sworn I had seen the same code in a similar question only a few weeks ago, and I was mistaken about the Exceptions. But I can't seem to find it on a search. Maybe you will be more successful than me; try searching.