Overloading/Overriding Problem

[Deepak Bajoria]

Hello ranchers,

Here this code:

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");
}
}
 

And the snippets:
Mammal h = new Horse();
Cattle c = new Horse();  
c.eat(h);

Outputs:
Mammal eats food

My first question is: Is eat() being overridden or overloaded? Arguments in subclasses are subclasses of those argument defined in superclasses.

I understand that c.eat(h) attaches it to mammal's version at compile time because of reference variable, but at runtime doesn't it know that the object held is of type horse. Since class Cattle doen't have eat(horse), it should have invoked eat(cattle).

Thanks in advance

Deepak

[Jamie MacDonald]

To override a method, the arguments must not change. Passing an argument which is a subtype is still a change in the argument. Therefore what you have is a case of overloading--NOT overriding. Which overloaded method is called is, as you point out, determined by the compiler at compile time. There is no overriding going on for the JVM to go picking a different method at run time.

[Milan Sutaria]

Deepak,
this is a nice question. The answer is Overload.

The expanded version of the classes is ...

class Mammal{
void eat(Mammal m){
System.out.println("Mammal eats food");}}
 
class Cattle extends Mammal{
//inherited from class Mammal
void eat(Mammal m){
System.out.println("Mammal eats food");}
 
void eat(Cattle c){
System.out.println("Cattle eats hay");}}
 
class Horse extends Cattle{
//inherited from class Mammal
void eat(Mammal m){
System.out.println("Mammal eats food");}
 
//inherited from class cattle
void eat(Cattle c){
System.out.println("Cattle eats hay");}
 
void eat(Horse h){
System.out.println("Horse eats hay");}} 
 
    

if don't believe it then try marking the methods final the code will still compile!! if the methods were overriden then marking them final will give compile errror.
Good luck for your exam!

[Deepak Bajoria]

OK, thank you Jamie and Milan for your explanations, got that.