Question

I cant figure out how the int 7 is consider as object in below example.

The sifer(7) is consider to be method sifer(Object o). I am not able to get it how this happened. In one of my java reference book it says Int can be boxed to an Integer and then “widened” to an object. I am not sure what that means.

 >> Class A 
class A { }     

 >> Class B 

class B extends A { }   
 >> Class ComingThru  

public class ComingThru {  
   static String s ="-";    
static void sifer(A[] ...a2)  
{  
    s = s + "1";  
}

static void sifer(B[] b1)  
{
    s += "3";  
}
static void sifer(Object o)   
{
    s += "4";  
}      

   public static void main(String[] args)   {
        // TODO Auto-generated method stub

    A[] aa= new A[2];  
    B[] ba = new B[2];  

    //sifer(aa);  
    //sifer(ba);  
    sifer(7);
    System.out.println(s);  


}  

}

Answer 1

Since there is no sifer(int) method, the compiler will try to find the “closest match”. In this case, the other 2 sifer methods take arrays as parameters, which an int clearly isn’t.

The last method, sifer(Object) can be applied to any objects, including an Integer so that’s the method that is used for sifer(7).

The reality is a little more complex, and the JVM will look for a matching mathod in the following order:

• an identity conversion
  • in your case: sifer(int) but there is no such method
• a widening primitive conversion
  • in your case: sifer(long) for example, but there is no such method
• a widening reference conversion
  • in your case: not applicable, int is not an object
• a boxing conversion optionally followed by widening reference conversion
  • in your case that’s what’s happening: int is boxed to Integer which is widened to Object
• an unboxing conversion optionally followed by a widening primitive conversion
  • in your case: not applicable