Introduction
In this article we discuss Enum as a new feature of Java.
What is Enum?
It is a data type containng a fixed set of constants. It can be used for directions (North, South, East and West), for days of the week (Sunday, Monday, Tuesday, Wednesday, Thursday, Friday and Saturday), etcetera. The enum constants are static and final implicitly. It is available from Java 5. An Enum can be thought of as a class with a fixed set of constants.
Important points
Some important points about Enum are:
- may implement many interfaces but cannot extend any class because it internally extends the Enum class.
- can have fields, constructors, and methods
- it improves type safety
- can be easily used in a switch
- can be traversed
Example
class EnumEx1
{
public enum Seasonlist
{
SUMMER, FALL, WINTER, SPRING,
}
public static void main(String args[])
{
for (Seasonlist sl: Seasonlist.values())
System.out.println(sl);
}
}
Output
![Fig-1.jpg]()
Values() method of enum
The Java compiler internally adds the values() method when it creates an enum. The values() method returns an array containing all the values of the enum.
Java compiler generates some code automatically
The Java compiler automatically creates a final and static class that extends the Enum.
Defining Enum
The enum can be defined within or outside the class because it is similar to a class.
Example
enum Seasonlist
{
SUMMER, FALL, WINTER, SPRING,
}
class EnumEx2
{
public static void main(String args[])
{
for (Seasonlist sl: Seasonlist.values())
System.out.println(sl);
}
}
Output
![fig-2.jpg]()
Initializing some specific value to constants
Constants of an enum can have some initial values, that start from 0, 1, 2, 3 and so on. But we can initialize a specific value of the enum by defining constructors and fields. As stated earlier, an enum contains constructors, methods and fields.
Example
The following example shows specification of an initial value to the enum constants.
class EnumEx3
{
enum Seasonlist
{
SUMMER(5), FALL(10), WINTER(15), SPRING(20);
private int val;
private Seasonlist(int val)
{
this.val=val;
}
}
public static void main(String args[])
{
for (Seasonlist sl: Seasonlist.values())
System.out.println(sl+" "+sl.val);
}
}
Output
![fig-3.jpg]()
Applying enum on switch statement
We can also apply an enum on a switch statement, as in the following example:
Example
class EnumEx4
{
enum DayList
{
SUN, MON, TUE, WED, THU, FRI, SAT
}
public static void main(String args[])
{
DayList day=DayList.SUN;
switch(day)
{
case SUN:
System.out.println("you are choosing Sunday");
break;
case MON:
System.out.println("You are choosing Monday");
break;
default:
System.out.println("You are choosing other day");
}
}
}
Output
![fig-4.jpg]()