Java Tutorial - Java Enum

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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/*from   w  w  w  . j a va  2s.  c om*/
}

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 .  j a va2s .co  m
  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 {/*from   ww  w  .j  a  va 2 s.  c o m*/
  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.

//from  ww  w.  j  a va  2 s  .co m
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.

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