What is the output of following program: public class test { public static void main(string[] args) { a a = new a(); a. methodb(); } } class a { public a() { system. out. println("a's constructor is executed"); } public void methoda() { system. out. println("methoda is executed"); } public void methodab() { system. out. println("a's methodab is executed"); } } class b extends a { private int num = 0; public b() { super(); system. out. println("b's constructor is executed"); } public b (int n) { num = n; system. out. println("b's constructor is executed"); } public void methodb() { system. out. println("num is " + num); system. out. println("methodb is executed"); } public void methodab() { system. out. println("b's methodab is executed"); } }