Enum - Constant Class

Enum in java is a data type that contains fixed set of constants.

It can be used for days of the week (SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY and SATURDAY) , directions (NORTH, SOUTH, EAST and WEST) etc. The java enum constants are static and final implicitly. It is available from JDK 1.5.

Java Enums can be thought of as classes that have fixed set of constants.

Points to remember for Java Enum

enum improves type safety
enum can be easily used in switch
enum can be traversed
enum can have fields, constructors and methods
enum may implement many interfaces but cannot extend any class because it internally extends Enum class

class EnumExample1{
public enum Season { WINTER, SPRING, SUMMER, FALL }
 
public static void main(String[] args) {
for (Season s : Season.values())
System.out.println(s);
 
}}


Java enum example: defined outside class
enum Season { WINTER, SPRING, SUMMER, FALL }
class EnumExample2{
public static void main(String[] args) {
Season s=Season.WINTER;
System.out.println(s);
}}  


Java enum example: defined inside class
class EnumExample3{
enum Season { WINTER, SPRING, SUMMER, FALL; }//semicolon(;) is optional here
public static void main(String[] args) {
Season s=Season.WINTER;//enum type is required to access WINTER
System.out.println(s);
}}


Initializing specific values to the enum constants
The enum constants have initial value that starts from 0, 1, 2, 3 and so on. But we can initialize the specific value to the enum constants by defining fields and constructors. As specified earlier, Enum can have fields, constructors and methods.

class EnumExample4{
enum Season{  
WINTER(5), SPRING(10), SUMMER(15), FALL(20);  
 
private int value;
private Season(int value){
this.value=value;
}
}
public static void main(String args[]){
for (Season s : Season.values())
System.out.println(s+" "+s.value);
 
}}

Constructor of enum type is private. If you don't declare private compiler internally creates private constructor.

class EnumExample5{
enum Day{ SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY}
public static void main(String args[]){
Day day=Day.MONDAY;
 
switch(day){
case SUNDAY:  
 System.out.println("sunday");
 break;
case MONDAY:  
 System.out.println("monday");
 break;
default:
System.out.println("other day");
}

}}