Задачу решил, но непонятен момент

public class Solution {

    public static void main(String[] args) {
        CTO cto = new CTO();
        System.out.println(cto);
    }

    public static interface Businessman {
        public void workHard();
    }

    public /*static*/ abstract class Human {
        public void workHard() {
            System.out.println("I am working");
        }
    }

    public static class CTO extends Human implements Businessman {

    }
}