Editor script private fields and method best practices

Hello,

What is the best approach to use private fields and methods of the in a custom editor script?

I mean:

 public class Foo
 {
    private int a;
    private float Method(int b)
   {
      ....
      ....
   }
 }

For design, I would like to keep private variable a and Method(int b). What could be the best approach to use this in its own editor? By reflection, for example?