Read EnumSet source code

//An enumeration-based Set, which is more efficient than HashSet most of the time.
//This class is an abstract class whose implementation classes are RegularEnumSet and JumboEnumSet.

//Create an enumeration that initially contains the specified elements (the methods with of are basically the same)
public static <E extends Enum<E>> EnumSet<E> of(E e) {
        EnumSet<E> result = noneOf(e.getDeclaringClass());
        result.add(e);
        return result;
    }

public static <E extends Enum<E>> EnumSet<E> noneOf(Class<E> elementType) {
        //Get enumeration according to elementType
        Enum[] universe = getUniverse(elementType);
        if (universe == null)
            throw new ClassCastException(elementType + " not an enum");
        // Call different implementations depending on the length
        if (universe.length <= 64)
            return new RegularEnumSet<>(elementType, universe);
        else
            return new JumboEnumSet<>(elementType, universe);
    }

// Contains all enumerations of the specified element type
public static <E extends Enum<E>> EnumSet<E> allOf(Class<E> elementType) {
        EnumSet<E> result = noneOf(elementType);
        result.addAll();
        return result;
    }

//Constructs an EnumSet that is the same as the specified enumeration.
public static <E extends Enum<E>> EnumSet<E> copyOf(EnumSet<E> s) {
        return s.clone();
    }

//An EnumSet initialized from the specified collection
public static <E extends Enum<E>> EnumSet<E> copyOf(Collection<E> c) {
        if (c instanceof EnumSet) {
            return ((EnumSet<E>)c).clone();
        } else {
            if (c.isEmpty())
                throw new IllegalArgumentException("Collection is empty");
            Iterator<E> i = c.iterator();
            E first = i.next();
            EnumSet<E> result = EnumSet.of(first);
            while (i.hasNext())
                result.add(i.next());
            return result;
        }
    }

//Include all elements not included in the specified set
public static <E extends Enum<E>> EnumSet<E> complementOf(EnumSet<E> s) {
        EnumSet<E> result = copyOf(s);
        result.complement();
        return result;
    }