How to determine the initialization order of object properties depending on different situations and context?

The question is quite simple, as can seem to much.

In General:

abstract class A {
 int a = 8;

 public A() {
show();
}

 abstract void show();
}

class B extends A {
 int a = 90;

 void show() {
 System.out.println("" + a);
}


}

And in the main method create an object of class B:

public static void main(String args[]) { 
 new B(); // output - 0
}

It is understandable, the superclass constructor will cause a polymorphic version of the show (especially in the base class it is abstract). The context variable is a change (one that is in the class B was not yet initialized to a value of 90, because it happens in the constructor?). But first, when you create an object B needs to be initialized its parent, all the fields that are there. When, then, the JVM has time to initialize the field to a zero when the command first calls the superclass constructor?

And that's all, if you slightly change the code in class B:

class B extends A {
 int x = 90; // changed the variable name!

 void show() {
 System.out.println("" + a); // 8
 }

The printed value of the variable a from the context object A - 8. Then I can still somehow understand that you initialize a variable before the call f-tsii show. Like that:

public A() {
 super(); // constructor Call Object and
 a = 8;
show();
 }

But when the time to initialize the field a in the context of object B, if at all, first the JVM is running on its base class? In General there are there subtleties?