Doubt in Overloading

[Abhijit Das]

 package pack2;
 
public class Overload {
    void sum(int a, int b){
    System.out.println("Primitive");
    }
    void sum(Integer a ,Integer b){
    System.out.println("Object");
    }
    public static void main(String[] args) {
Overload ob = new Overload();
        Integer x= new Integer(10);
        int y = 20;
        ob.sum(10,20);
        //ob.sum(x,y); ERROR,
    }
 
}
   

The error message comes for the comment line as " Ambiguious for the type overload" .
Now , if I pass the explicit values , no error comes. But ambiguity rises as i pass the variables.
What is the difference between this two method calling.

thanks
Abhijit

[Ian Edwards]

Because boxing or unboxing is required to satisfy either of the signatures the compiler doesn't know which method it should call.

[Abhijit Das]

hello, Ian
I am not cleared. Why it is not automatically unboxed or boxed for method invocation. If I comment either of methods, then it is working.

Thanks

[Jesus Angeles]

As Ian has mentioned already,

for

ob.sum(10,20)

the compiler is passed with implied 2 int primitives. Therefore, the compiler knows which method to call, which is the

sum(int a, int b)

However, for the

ob.sum(x,y);

you passed an int and and Integer. The compiler doesnt know which of the 2 methods to call:

sum(int a, int b)
or
sum(Integer a ,Integer b)

If you are still confused, try think like a compiler. If you are the compiler, how you know which of the 2 overloaded methods would you call if you are given

ob.sum(x,y)

?

[Dean Jones]

Are these examples of overloading,

void sum(int a, int b){    System.out.println("Primitive");    }    void sum(Integer a ,Integer b){    System.out.println("Object");    }