Question about Java overloading & dynamic binding

Как в приведенном ниже коде первая и вторая операторы печати распечатывают SubObj ?? Do top and sub point to the same Sub class?

class Top {
    public String f(Object o) {return "Top";}
}

class Sub extends Top {
    public String f(String s) {return "Sub";}
    public String f(Object o) {return "SubObj";}
}

public class Test {
    public static void main(String[] args) {  
        Sub sub = new Sub();
        Top top = sub;
        String str = "Something";
        Object obj = str;


        System.out.println(top.f(obj));
        System.out.println(top.f(str));
        System.out.println(sub.f(obj));
        System.out.println(sub.f(str));
    }
}

Above code returns below result.

SubObj
SubObj
SubObj
Sub