Collections - The Java Programming Language - page 880

21.9. enum Collections
Two collections, EnumSet and EnumMap , are specifically designed for working
efficiently with enum constants.
21.9.1. EnumSet
The abstract class EnumSet<Eextends Enum<E>> represents a set of elements
that are all enum constants from a specific enum type. Suppose you were
writing a reflection related API , you could define an enum of the different
field modifiers, and then have your Field class return the set of modifiers
applicable to that field:
enum FieldModifiers { STATIC, FINAL, VOLATILE, TRANSIENT }
public class Field {
public EnumSet<FieldModifiers> getModifiers() {
// ...
}
// ... rest of Field methods ...
}
In general, whenever an enum represents a set of flags or "status bits,"
then you will probably want to group the set of flags applicable to a given
element in an enum set.
EnumSet objects are not created directly but are obtained from a number
of static factory methods in EnumSet .
public static <E extends Enum<E>> EnumSet<E> allOf(Class<E> enumType)
Creates an EnumSet containing all the elements of the given
enum type.