Overloading

[Smitha Ballikar]

  
class Mammal{
 void eat(Mammal m){
 System.out.println("Mammal eats food");
 }
}

class Cattle extends Mammal{
 void eat(Cattle c){
 System.out.println("Cattle eats hay");
 }
}
 
class Horse extends Cattle {
 void eat(Horse h){
 System.out.println("Horse eats hay");
 }
}

public class Test{
public static void main(String[]args){
 Mammal h = new Horse();
 Cattle c = new Horse();
 c.eat(h);
 }
}
1.prints "Mammal eats food".
2.prints "Cattle eats hay"
3.prints "Horse eats hay"
4.Class cast exception at runtime
 
Answer given:
1.prints "Mammal eats food".
 
I feel 3 since cattle object c is pointing to horse object .When we call a method using c refernce like c.eat(h) and also horse object is passed so the eat method of horse will be called
 
Why answer is 1.
 
Please explain??
 
Thanks..
 

[Arulkumar Gopalan]

The subject of this question gives the answer.
Overloading! i.e execution of methods is decided at compile time itself, not at runtime.
So, It was already decided that Mammal's method will be executed irrespective of which object is being referred by "h".
[ August 09, 2005: Message edited by: Arulkumar Gopalan ]

[Smitha Ballikar]

So, It was already decided that Mammal's method will be executed irrespective of which object is being

Hi Arul,

I still didnt get the point.Even if it is decided at compile time Why the method of class mammal is executed.Can you please explain in depth..
Thanks..

[Arulkumar Gopalan]

- Overloading is driven by parameters declared in the methods
- Objects are created at run time only.
- Compiler has no idea on what object is being referred by a reference variable.
Are we clear on these points?

According to the compiler, the method to be called is which ever has Mammal's reference as parameter, no matter what does it actually refer. So, it does execute Mammal's method.

[Smitha Ballikar]

Hi Arul,

Thanks for the explanation...
I did understand that the method is called based on the type of parameter passed.I am also clear that objects are created at runtime.

But I have a small confusion in my concept. When do we actually check the type of object being referenced and call the method of that particular object??Is it in overriding?

Thanks..

[Arulkumar Gopalan]

When do we actually check the type of object being referenced and call the method of that particular object??Is it in overriding

Yes, it is overriding, which is acting on the principle "A super class variable can refer a sub class object". So, depending upon the object being referred the appropriate method will be invoked at run time.

Little thing to remember everything:
Overloading: Compile time polymorphism
Overriding: Runtime polymorphism
[ August 09, 2005: Message edited by: Arulkumar Gopalan ]

[Smitha Ballikar]

Hi Arul,

Got it Now!!!

Thanks..