Wat?

Main.java

package bug;

public class Main {
    public static void main (String[ ] args) {
        SuperClass a = new SuperClass ( ); // 1
        SubClass   b = new SubClass ( );   // 2 e 1.0
        SuperClass c = new SuperClass ( ); // 3
        SubClass   d = new SubClass ( );   // 4 e 2.0

        a.printSelf (c); // 3
        c.printSelf (a); // 1

        a.printSub (b); // 1.0 e 2
        a.printSub (d); // 2.0 e 4
    }
}

// estado é privado e inteiro
class SuperClass {
    private static int serial = 0;
    private        int state;

    private synchronized static void create (SuperClass object) {
        serial += 1;
        object.state = serial;
    }

    public SuperClass ( ) {
        create (this);
    }

    public void printSelf (SuperClass object) {
        System.out.println (object.state);
    }

    public void printSub (SubClass object) {
        System.out.print (object.state + " | ");
        printSelf ((SuperClass) object);
    }
}

// estado é público e double
class SubClass extends SuperClass {
    private static double serial = 0.0;
    public         double state;

    private synchronized static void create (SubClass object) {
        serial += 1;
        object.state = serial;
    }

    public SubClass ( ) {
        super ( );
        create (this);
    }
}

// end