Hello guys, happy new year.
 Well, a very basic question. I make a class objekt that lookes
something like this :

public class circle {

 public static final PI = 3.14159;
 public double r;
 public double area(double r) {
       return r*r*PI;
 }
}

and then from somewhere else I do :

circle.r = 5;
double area = circle.area();  <--- this gives me a compilation error,
it wants me to specify circle.area(5). I thought

that it was legitamet code to leave it at (). Is'nt it what object
oriented code was all about, i have already defined the objects
variable r to bee 5, shouldent need to further specify
circle.area(5).
 Thank you for any response in advance.