Java: object initialization sequence

There is code that is set as a task for junior Java developers. I have been using Java for five years, and this piece of code is completely confusing to me:

public class Main {

    String variable;

    public static void main(String[] args) {
        System.out.println("Hello World!");
        B b = new B();
    }

    public Main(){
        printVariable();
    }

    protected void printVariable(){
        variable = "variable is initialized in Main Class";
    }
}

public class B extends Main {

    String variable = null;

    public B(){
        System.out.println("variable value = " + variable);
    }

    protected void printVariable(){
        variable = "variable is initialized in B Class";
    }
}

The output will be:

Hello World!
variable value = null

But if we change String variable = null;to String variable;, we get:

Hello World!
variable value = variable is initialized in B Class

The second conclusion is more clear to me. So, as far as I know the initialization sequence in Java, for example:

• We go to the root of the class hierarchy (for Java, it is always the Object class) when we come to this root parent class:
  • All static data fields are initialized;
  • All static field initializers and static initialization blocks are executed;
  • All non-static data fields are initialized;
  • All non-static field initializers and non-static initialization blocks are executed;
  • :
• .

, this -

, , ​​:

• B;
• part Main;
• main.variable null;
• Main;
• b.printVariable() Main; ( main.printvariable? this .)
• field b.variable " B-"
• B;
• b.variable , ?;
• B

, - , . String variable = null; String variable; .