How does the JVM initiate the fields in super and sub classes?

Question

Can any body tell why the output of following code is "null"? And what is the best way to construct a complex Object and delegate the details to their subclasses?

package com.test;

public class ClassA {

    ClassA() {
        initHeader();
        initBody();
        initFooter();
    }

    void initHeader() {}

    void initBody() {}

    void initFooter() {}

    public static void main(String[] args) {
        ClassB a = new ClassB();
        System.out.println(a.obj);
    }
}

class ClassB extends ClassA {

    public Object obj = null;

    ClassB() {
        super();
    }

    void initHeader() {
        obj = new Object();
    }

}

Answer 1

First, the fields of ClassA are initialized.

The constructor of ClassA is then called, calling ClassB.initHeader().

After that, fields of ClassB are initialized overriding what initHeader() had done.