// filename RollCall.java
//
// example of upcasting, polymorphism, interface
//
// output will be
// Joe is present!
// Tony is present!
// Jeremy is present!

import java.util.*;      // needed for Vector

// inteface Person, forces class to implement getName method
interface Person {
    String getName();   // force any class to implement this method
}

// class Student implements Person
class Student implements Person {
    String name;

    Student(String n) {      //  constructor
	name = n;
    }

    public String getName() {   // implementation of getName from Person interface
        return name;
    }
}

// class RollCall, test drive interface Person and class Student
// upcasting Student to Person is ok because a Student is a Person
// polymorphism behavior, person is retrieved from the Vector upcast as a Student
// when person.getName() method is called, the correct name is printed

public class RollCall {
    public static void main(String[] args) {
	Vector classRoom = new Vector();

        // add students in the class room
        classRoom.addElement(new Student("Joe"));
        classRoom.addElement(new Student("Tony"));
        classRoom.addElement(new Student("Jeremy"));

        // lets find out who's in the class romm
        for (int i = 0; i < classRoom.size(); i++) {
	    Person person = (Student)classRoom.elementAt(i);        // upcasting Student to Person
            System.out.println(person.getName() + " is present!");  // polymorphism behavior
        }
    }
}