这个运行结果是什么啊

interface Result{

double calculate(double x,double y);       

}

class R {

  double calculate(int x,double y) {

        return x * y;            

 }         

}

class RA extends R implements Result{

  public double calculate(double x,double y){

       return x / y;             

}      

public double calculate(int x,int y){             

       return x - y;         

 }  

}

class Test_2 {

 public static void main(String args[]){                     

      Result r = new RA();                  

      System.out.println(r.calculate(12, 6));

      RA s = (RA) r;              

      System.out.println(s.calculate(12, 6));                    

      R rr = new RA();                  

      System.out.println(rr.calculate(12, 6));            

}

static {             

      int a = 50 / 2 + 19 % 4;               

      System.out.printf("a=%+d\n",a);              

 }                      

}

a=+28
2.0
6.0
72.0