In Java, an enum (enumeration) is a special type used to define a fixed set of constants. Enums make programs easier to read, understand, and maintain.
An enum is useful when a variable should contain only a limited number of predefined values, such as days, months, directions, or order statuses.
enum Day {
MONDAY,
TUESDAY,
WEDNESDAY,
THURSDAY,
FRIDAY,
SATURDAY,
SUNDAY
}Here, Day can represent one of the seven days.
Declare an enum and use its constants with the enum name.
enum Day {
MONDAY, TUESDAY, WEDNESDAY,
THURSDAY, FRIDAY, SATURDAY, SUNDAY
}
public class Main {
public static void main(String[] args) {
Day today = Day.MONDAY;
System.out.println(today);
}
}MONDAYDay.MONDAY.
Enum constants are fixed values declared inside an enum. By convention, their names are written in uppercase.
enum TrafficLight {
RED, YELLOW, GREEN
}
public class Main {
public static void main(String[] args) {
TrafficLight light = TrafficLight.GREEN;
System.out.println("Signal: " + light);
}
}Signal: GREENEnums can be checked using if-else statements.
enum Level {
LOW, MEDIUM, HIGH
}
public class Main {
public static void main(String[] args) {
Level level = Level.HIGH;
if (level == Level.HIGH) {
System.out.println("High level selected");
} else {
System.out.println("Another level selected");
}
}
}High level selectedAn enum works well with a switch statement when different constants require different actions.
enum Day {
MONDAY, TUESDAY, WEDNESDAY
}
public class Main {
public static void main(String[] args) {
Day day = Day.MONDAY;
switch (day) {
case MONDAY:
System.out.println("Start of the week");
break;
case TUESDAY:
System.out.println("Second day");
break;
case WEDNESDAY:
System.out.println("Middle of the week");
break;
}
}
}Start of the week
The values() method returns an array containing
all enum constants in their declared order.
enum Color {
RED, GREEN, BLUE
}
public class Main {
public static void main(String[] args) {
for (Color c : Color.values()) {
System.out.println(c);
}
}
}RED
GREEN
BLUE
The valueOf() method converts an exact constant
name into its corresponding enum value.
enum Size {
SMALL, MEDIUM, LARGE
}
public class Main {
public static void main(String[] args) {
Size s = Size.valueOf("MEDIUM");
System.out.println(s);
}
}MEDIUMSize.valueOf("medium") throws
IllegalArgumentException.
The ordinal() method returns the zero-based
position of an enum constant in its declaration.
enum Level {
LOW, MEDIUM, HIGH
}
public class Main {
public static void main(String[] args) {
System.out.println(Level.LOW.ordinal());
System.out.println(Level.MEDIUM.ordinal());
System.out.println(Level.HIGH.ordinal());
}
}0
1
2An enum can have a constructor to store additional information for each constant. Enum constructors cannot be public or protected.
enum Course {
JAVA("Programming"),
PYTHON("Programming"),
HTML("Web Development");
private String category;
Course(String category) {
this.category = category;
}
public String getCategory() {
return category;
}
}
public class Main {
public static void main(String[] args) {
System.out.println(Course.JAVA.getCategory());
System.out.println(Course.HTML.getCategory());
}
}Programming
Web DevelopmentEnums can contain fields, constructors, and methods, just like classes.
enum Status {
PENDING("Waiting"),
APPROVED("Accepted"),
REJECTED("Declined");
private String message;
Status(String message) {
this.message = message;
}
public String getMessage() {
return message;
}
}
public class Main {
public static void main(String[] args) {
Status s = Status.APPROVED;
System.out.println(s);
System.out.println(s.getMessage());
}
}APPROVED
Accepted
Enum constants are unique instances. You can compare them
using == or equals().
enum Direction {
NORTH, SOUTH, EAST, WEST
}
public class Main {
public static void main(String[] args) {
Direction d1 = Direction.NORTH;
Direction d2 = Direction.NORTH;
Direction d3 = Direction.SOUTH;
System.out.println(d1 == d2);
System.out.println(d1 == d3);
}
}true
false| Enum | String |
|---|---|
| Represents predefined constants | Stores text |
| Restricts values to declared constants | Can contain many different text values |
Example: Day.MONDAY |
Example: "Monday" |
| Useful for fixed choices | Useful for general text |
Weekday with all seven days.Season with four seasons and print one season.TrafficLight and use a switch statement to display an instruction.values() to print all constants of a Month enum.valueOf() to convert the string "LARGE" into an enum value.ordinal() to display the positions of three enum constants.PaymentStatus enum with PENDING, PAID, and FAILED.Course enum with a field storing each course's fee and a method to display it.==.OrderStatus and print a suitable message for each status.Select the correct answer for each question.