code: public static Number sum( Number n1 , Number n2 )
      {
          Class<?> type = getComputationType(n1,n2);
          Number val1 = convertTo(n1,type);
          Number val2 = convertTo(n2,type);
  
          if (type == Long.class)
              return Long.valueOf(val1.longValue()+val2.longValue());
          
          return new Double(val1.doubleValue()+val2.doubleValue());
      }
docs: Sum two numbers