ENUMERATED TYPESENUMERATED TYPESJava Basics

Enumerated Type TopicsEnumerated Type Topics

• Why use them?• Defining an enumerated type• Using an enumerated type• Advanced features

Before Enumerated TypesBefore Enumerated Typespublic 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 - definingEnumerated 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 enumSimilar to class, this is a new data type!

fixed set of possiblevalues – in ALL_CAPSbecause they are likeconstants. In braces – similar to class definition, but withspecial syntax for body.

enum name – it’s a type!

name of variable

Enumerated Types - usingEnumerated 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 theoptions for FilingStatus

Enumerated Type - ExampleEnumerated Type - Examplepublic 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 continuedExample continuedpublic class InvoiceTracker {

ArrayList<Invoice> invoices;

public void addInvoices() {

invoices = new ArrayList<Invoice>();

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 ExampleAnother 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 AppointmentRevised Appointmentpublic 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();}

}