// Trace1 Example.

// Draw the reference diagram, trace the instance
// variable changes and predict the output.

public class Main1
{
    public static void main(String[ ] args)
    {
        A a1 = new A( );
        A a2 = new A(10, 11);
        B b1 = new B(20, 21);

        a1.f(0);
        a2.f(1);
        b1.f(2);

        System.out.println(a1);
        System.out.println(a2);
        System.out.println(b1);
    }
}

// Output:
11x3
18x11
28x23x3