Enumerated Types

1
Enumerated Types

• Java Basics

2
Enumerated Type Topics

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

3
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 remindTuesdayPatient
s() if (whichDay 2)
System.out.println("Remember your
appointment!") public static void
main(String args) Appointment appointment
new Appointment() appointment.scheduleAppoi
ntment() appointment.remindTuesdayPatients()

4
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

keyword to indicate this is enumerated type
name of the enum Similar to class, this is a new
data type!
typically public, so can access outside this
class
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 its a type!
name of variable
5
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
6
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

7
Example continued

• public class InvoiceTracker
• ArrayListltInvoicegt invoices
• public void addInvoices()
• invoices new ArrayListltInvoicegt()
• 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()

8
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

9
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()