Which class in Java implements the abstract class EnumSet?

I see that EnumSet.of() returns an instance of an object of the type EnumSet. But I am not able to figure out which class actually implements this abstract class? How can you get an instance of the abstract type EnumSet, when you have not subclassed it?

Here is are 2 classes in java which extends EnumSet

1. RegularEnumSet
2. JumboEnumSet

You can create the instance using EnumSet's static methods like EnumSet#noneOf, EnumSet#allOf etc. Which actually returns the instance of RegularEnumSet or JumboEnumSet depending on the condition. EnumSet#of internally calls EnumSet#noneOf.Please refer the below code from Java to see how EnumSet#noneOf works

public static <E extends Enum<E>> EnumSet<E> noneOf(Class<E> elementType) {
    Enum<?>[] universe = getUniverse(elementType);
    if (universe == null)
        throw new ClassCastException(elementType + " not an enum");

    if (universe.length <= 64)
        return new RegularEnumSet<>(elementType, universe);
    else
        return new JumboEnumSet<>(elementType, universe);
}