Fix the Java code below with Casting method:

public interface Flyer {

public void fly();

}

public class Bird implements Flyer {

public void fly() {

System.out.println("flap flap");

}

}

public class Duck extends Bird {

public void quack() {

System.out.println("Quack quack");

}

}

public class Swan extends Bird {

public void glide() {

System.out.println("I am like SO graceful");

}

public static void main(String[] args) {

Swan s = new Swan();

Bird b = s;

Duck d = b;

d.quack();

}

}