Java – internal static class field visibility

I have two classes, as follows

public class A{

  private static class B{
   private static int s1;
   private static int s2;
   private int x;

  }
}

In class B, all fields are private and should not be accessed in class A But there is a 'mystery', static fields can be in class A and class B

private int x

Not accessible My question is why private static fields can be accessed in class a?

Note: my class B is static and its constructor is private

Solution

In addition to the answer given by @ UWE plonus (1), I can assume that you try to access the non static field X through class B without creating an instance, that is

B.x = 5;

You must create an instance of Claas B to access its instance members, i.e

new B(). x = 5;