How to access a private field in a private field in another class using Java

I am clear that accessing a private field in Java could be easily achieved by using Reflection. As is shown in posts as How to read the value of a private field from a different class in Java? and there are many.

To achieve that , the critical move is to set accessibility.

Field f = obj.getClass().getDeclaredField("aaa"); 
f.setAccessible(true);

But in my case, the situation is like:

class A{
 private B b;

 class B{
   private String value;
 }
}

and I want to get value of a.b.value in another class. When I was trying, I intended to do it as

Field f = obj.getClass().getDeclaredField("b"); 
f.setAccessible(true);
B b = f.get(obj);
Field f2 = b.getClass().getDeclaredField("value");
String value = f2.get(b);

Which doesn't work out because B could not be declared out of A. Do I have other options if Class A can not be modified?