public class OverloadingTest {
    public static int sum(int ...a){
        int sum=0;
        for(int i : a){
            sum += i;
        }
        System.out.print("this is variant args//");
        return sum;
    }

    public static double sum(double a, double b) {
        return a + b;
    }

    public static void main(String[] args) {
        System.out.println(sum(1.5, 2.5));
        System.out.println(sum(10, 20));
        System.out.println(sum(10, 20,30));
    }
}

4.0
this is variant args//30
this is variant args//60

4.0
30.0
this is variant args//60

int x = sum(10, 20);

System.out.println(sum(10, 20));

Primitive widening uses the smallest method argument possible
Wrapper type cannot be widened to another Wrapper type
You can Box from int to Integer and widen to Object but no to Long
Widening beats Boxing, Boxing beats Var-args.
You can Box and then Widen (An int can become Object via Integer)
You cannot Widen and then Box (An int cannot become Long)
You cannot combine var-args, with either widening or boxing