public class test {

    static class father {

        void run() {

            System.out.println("father run");

        }

    }

    static class son extends father{

        void run() {

            System.out.println("son run");

        }

    }

    public void sayHello(son son) {

        System.out.println("son");

    }

    public void sayHello(father father) {

        System.out.println("father");

    }

    public static void main(String[] args) {

        father a = new son();

        a.run();

        test t = new test();

        t.sayHello(a);

        System.out.println(a.getClass());

    }

}