Java Enum

public enum Direction{initial, up, down}

public static void main(String[] args) {
  for (Direction d: Direction.values())
    System.out.println(d.name());

  // EnumSet
  EnumSet eSet = EnumSet.allOf(Direction.class);
  for (Direction d: eSet)
    System.out.println(d.name());

  // EnumMap
  EnumMap eMap = new EnumMap(Direction.class);
  eMap.put(Direction.initial, "to be expanded");
  eMap.put(Direction.up, "go upwards");
  eMap.put(Direction.down, "go downwards");
  for (Direction d: Direction.values())
    System.out.println(d.name() + ": " + eMap.get(d));

  // assignment
  Direction d = Direction.initial;

  // in switch
  switch(d) {
  case initial:
    ...
  case up:
    ...
  case down:
    ...
  } 
}
1. Enum can be used instead of public static final constants sometimes...
2. Enum can not extend or be extended...