public class Greeter
  implements EntranceListener
{
  private String welcome(Roommate rm)         { return "'Sup?"; }
  private String welcome(Parent p)            { return "Please insert cash or select payment type."; }
  private String welcome(Robber r)            { return "Good luck; we're in college."; }
  private String welcome(SignificantOther so) { return null; }
  private String welcome(PersonType pt)       { return "Welcome to our house." }

  public void
  personEntered(PersonType person)
  {
    String salutation = welcome(person);
    if (salutation != null) System.out.println(salutation);
  }
}