I have some problems with manipulating an object.

[mohed.haidar]

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.

 

[Owen Jacobson]

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;

This defines a member variable named 'r'.

  public double area(double r) {

This defines a method taking a parameter named 'r', unrelated to the
member variable. You probably meant
public double area () {
or more conventionally
public double getArea () {

        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).

In Java, local variable names and parameter names hide member
variables with the same name. The following program is exactly
equivalent to your original program, but illustrates why you get an
error:

public class circle {
public static final PI = 3.14159;
public double r;
public double area(double r2) {
return r2*r2*PI;
}
}

-o

 

[Patricia Shanahan]

In addition to Owen's comments, PI needs a type. On the other hand, you
should probably get rid of it. Math.PI is a far closer approximation to pi.

Patricia