covariant doubt

[raja kanak]

class SuperCafe4Java {
public Object get (Object o) {
return ("SuperCafe4Java");
}
}
 
class SubCafe4Java extends SuperCafe4Java {
public String get (String o) {
return ("SubCafe4Java");
}
}
public class TestCafe4Java {
public static void main (String[] arguments) {
SuperCafe4Java superFoo;
SubCafe4Java subFoo;
 
superFoo = new SubCafe4Java();
System.out.println (superFoo.get("super"));
 
subFoo = new SubCafe4Java();
superFoo = subFoo;
System.out.println (superFoo.get("super"));
}
}    

I guess answer would be
SubCafe4Java
SubCafe4Java
But when i run the programme it shows
SuperCafe4Java
SuperCafe4Java

We are calling
superFoo.get("super") i.e., superclass reference with subclass object in it, also parameter "super" is a String object. So it is more appropriate to call subclass get() but why superclass get() called?

I can't understand.... thanks in advance for any help...

[hemadri raju]

when you are redifining the function in the child class you are not overloading the base class function, because the base class is having parameter as Object but child class is having parameter as String. So it is not covariant return.

and when you are calling the funciton you are calling using the base class version. so always function of the base class is getting called

[Sanjeev Singh]

Where are the covariant retrun types?
I think you got confused and pretends to think that the methods are overridded.Infact the methods are overloaded in first two classes.To make it a valid overrided method with covariant return type make change as

class SuperCafe4Java {
public Object get ([B]String o[/B]) {[B]//Change here[/B]
return ("SuperCafe4Java");
}
}
 
class SubCafe4Java extends SuperCafe4Java {
public String get (String o) {
return ("SubCafe4Java");
}
}
public class TestCafe4Java {
public static void main (String[] arguments) {
SuperCafe4Java superFoo;
SubCafe4Java subFoo;
 
superFoo = new SubCafe4Java();
System.out.println (superFoo.get("super"));
 
subFoo = new SubCafe4Java();
superFoo = subFoo;
System.out.println (superFoo.get("super"));
}
} 

[Bob CHOI]

  
  
public Object get (Object o) {return ("SuperCafe4Java");}
public String get (String o) {return ("SubCafe4Java");}
 

2nd one can't override 1st because the argument signature is different even thought String is subclass of Object, hence it's called overloaded - name reuse but new method.

  
 
superFoo = new SubCafe4Java();
System.out.println (superFoo.get("super")); 
  

Now superFoo owns only the 1st method, it's always legal - here the argument Object is subcast to String again when get("super") being called.

finally it prints out "SuperCafe4Java";

[raja kanak]

thanks a lot to all.