Задачу решил. Вопрос про toString

public static Map<String, String> createPeopleMap() {
   Map<String,String> people = new HashMap<>();
    for (int i = 0; i < 4; i++) {
        people.put("Джон" + i, "Иванов");
    }
    for (int i = 0; i < 4; i++) {
        people.put("Джон", "Иванов" + i);
    }
people.put("Иван", "Джонович");
    people.put("Рулон", "Обоевич");
    return people;
}

public static void printPeopleMap(Map<String, String> map) {
    for (Map.Entry<String, String> s : map.entrySet()) {
        System.out.println(s.getKey() + " " + s.getValue());
    }
}