ENUMERATED TYPES Java Basics

Enumerated Type Topics Why use them? Defining an enumerated type Using an enumerated type Advanced features

Before Enumerated Types public class Appointment { private int whichDay; private int scheduleLocation; public void scheduleAppointment() { System.out.println("Enter 1 for Monday, 2 for Tuesday or 3 for Thursday: "); Scanner scan = new Scanner(System.in); whichDay = scan.nextInt(); System.out.println("Enter 1 for Golden, 2 for Boulder or 3 for Lafayette: "); scheduleLocation = scan.nextInt(); } public void remindTuesdayPatients() { if (whichDay == 2) System.out.println("Remember your appointment!"); } public static void main(String[] args) { Appointment appointment = new Appointment(); appointment.scheduleAppointment(); appointment.remindTuesdayPatients(); }

Enumerated Types - defining An enum type is a type whose fields consist of a fixed set of constants. Define the type: public enum FilingStatus {SINGLE,MARRIED}; Declare a variable of this type: FilingStatus status; typically public, so can access outside this class keyword to indicate this is enumerated type name of the enum Similar to class, this is a new data type! fixed set of possible values – in ALL_CAPS because they are like constants. In braces – similar to class definition, but with special syntax for body. enum name – it’s a type! name of variable

Enumerated Types - using To specify a value, must include the name of the enumerated type if (status == FilingStatus.SINGLE)... Can use in another class, if specify class name in which enum is declared: if (status == TaxReturn.FilingStatus.SINGLE)... An enumerated type variable can be null variable of type FilingStatus without this, SINGLE would not be recognized (would look like a regular constant) must be one of the options for FilingStatus

Enumerated Type - Example public class Invoice { public enum Status { PAID, UNPAID, WRITE_OFF }; Status status; double balance; public Invoice(double balance) { this.balance = balance; status = Status.UNPAID; } public void updateStatus(Status status) { this.status = status; } public String toString(){ return "Invoice balance: " + balance + " status " + status; }

Example continued public class InvoiceTracker { ArrayList invoices; public void addInvoices() { invoices = new ArrayList (); Invoice inv = new Invoice(300); inv.updateStatus(Invoice.Status.PAID); invoices.add(inv); inv = new Invoice(650); inv.updateStatus(Invoice.Status.WRITE_OFF); invoices.add(inv); } public void displayInvoices() { for (Invoice inv : invoices) System.out.println(inv); } public static void main(String[] args) { InvoiceTracker track = new InvoiceTracker(); track.addInvoices(); track.displayInvoices(); }

Another Example Enumerated types can be defined in their own file Enumerated types can define methods, useful for converting to String, etc. public enum DayOfWeek { MONDAY ("Monday"), TUESDAY ("Tuesday"), WEDNESDAY ("Wednesday"), THURSDAY ("Thursday"), FRIDAY ("Friday"); private String value; DayOfWeek (String aValue) { value = aValue; } public String toString() { return value; }

Revised Appointment public class Appointment { //private int whichDay; private DayOfWeek whichDay; private int scheduleLocation; public void scheduleAppointment() { System.out.println("Enter day of week: "); Scanner scan = new Scanner(System.in); String day = scan.next(); whichDay = DayOfWeek.valueOf(day.toUpperCase()); } public void remindTuesdayPatients() { if (whichDay == DayOfWeek.TUESDAY) System.out.println("Remember your appointment!"); } public static void main(String[] args) { Appointment appointment = new Appointment(); appointment.scheduleAppointment(); appointment.remindTuesdayPatients(); }