import java.util.*; class Person { String name; } class Teacher extends Person { String grade; } class Census { public static void register(List<? extends Person> people) { for (Person p: people) { System.out.println(p.name); } // people.add(new Person()); // you can't do that } } class G14 { public static void main( String[] args ){ List<Teacher> record = new LinkedList<Teacher>(); // fill teachers' record Census.register(record); } }