Java Tutorial - Java Enum

An enumeration is a list of named constants.

Syntax

An enumeration is created using the enum keyword.

For example, here is a simple enumeration:

enum Direction { 
 East, South, West, North
}

The identifiers East, South are called enumeration constants. Enumeration constants is implicitly declared as a public, static final member of Direction.

Enum type variable

Once you have defined an enumeration, you can create a variable of that type.

Even though enumerations define a class type, you do not instantiate an enum using new.

The following code declares ap as a variable of enumeration type Direction:

Direction ap;

Because ap is of type Direction, the only values that it can be assigned are those defined by the enumeration. For example, this assigns ap the value South:

ap = Direction.South;

Compare

Two enumeration constants can be compared for equality by using the == relational operator.

// An enumeration of direction varieties. 
enum Direction {
 East, South, West, North/*fromwww.java2s.com*/
}
public class Main {
 public static void main(String args[]) {
 Direction dir = Direction.South;
 System.out.println("Value of dir: " + dir);
 dir = Direction.South;
 if (dir == Direction.South){
 System.out.println("ap contains GoldenDel.\n");
 }
 }
}

The code above generates the following result.

Enum Switch

An enumeration value can also be used to control a switch statement.

enum Direction {//www.java2s.com
 East, South, West, North
}
public class Main {
 public static void main(String args[]) {
 Direction dir = Direction.South;
 switch (dir) {
 case South:
 System.out.println("south");
 break;
 case East:
 System.out.println("East");
 break;
 case West:
 System.out.println("West");
 break;
 case North:
 System.out.println("North.");
 break;
 }
 }
}

The code above generates the following result.

Java Enum values() / valueOf() Methods

All enumerations automatically contain two predefined methods: values() and valueOf().

Their general forms are:

public static enum-type[ ] values() 
public static enum-type valueOf(String str)

The values() method returns an array that contains a list of the enumeration constants. The valueOf() method returns the enumeration constant whose value corresponds to the string passed in str.

The following program demonstrates the values() and valueOf() methods:

enum Direction {/*fromwww.java2s.com*/
 East, South, West, North
}
public class Main {
 public static void main(String args[]) {
 Direction all[] = Direction.values();
 for (Direction a : all){
 System.out.println(a);
 }
 System.out.println();
 Direction dir = Direction.valueOf("South");
 System.out.println(dir);
 }
}

The code above generates the following result.

Compare enum

The following code shows how to compare enum data type.

//fromwww.java2s.com
enum Week {
 Monday, Tuesday, Wednesday, Thursday, Friday, Saturaday, Sunday
}
public class Main {
 public static void main(String args[]) {
 Week day1, day2, day3;
 day1 = Week.Monday;
 day2 = Week.Tuesday;
 day3 = Week.Friday;
 // 
 if (day1.compareTo(day2) < 0)
 System.out.println(day1 + " comes before " + day2);
 if (day2.compareTo(day3) > 0)
 System.out.println(day2 + " comes before " + day3);
 if (day1.compareTo(day3) == 0)
 System.out.println(day1 + " equals " + day3);
 }
}

The code above generates the following result.