Enum is a special data type that can be set to one of predefined constants.

public enum Day {

MONDAY, TUESEDAY, WEDNESDAY, THURSTDAY, FRIDAY, SATURDAY, SUNDAY

}

In code it is used like:

Day d = Day.SATURDAY;
System.out.println(d);

Each enum constant can declare its value.

public enum Color {

RED (1),
GREEN (2),
BLUE (3);

private int colorId;

private Color(int i) {
this.colorId = i;
}

public int getColorId() {
return colorId;
}

public static Color getColor(int id) {
if (id == 1) {
return Color.RED;
} else if (id == 2) {
return Color.GREEN;
} else if (id == 3) {
return Color.BLUE;
}
return null; // should not happen
}

}

Use the enum in code:

System.out.println(Color.GREEN + " = " + Color.GREEN.getColorId());
System.out.println(3 + " = " + Color.getColor(3));