public static void LiveADay(object obj)
{
// declare Person class reference variable
Person person = (Person)obj;
// declare IPerson interface reference variable
IPerson iPerson = (IPerson)obj;
// declare IStudent interface reference variable
// initialize to null because we do not know if obj is Student or Teacher
IStudent iStudent = null;
// notice how we can use the IPerson interface to call Eat() for both Student and Teacher
// because that method is defined in the shared interface
iPerson.Eat();
// notice how we can use a Person reference to call Work()
// because the virtual method is defined in the shared Person class
// even though the method implementation is different between the 2 classes
person.Work();
// but because Party() is only a member of Student
// as a result of inheriting IStudent
// we need to ensure obj is a Student
if (obj.GetType() == typeof(Student))
{
// we use an IStudent reference to call Party()
iStudent = (IStudent)person;
iStudent.Party();
}
}