Search code examples
javaenumsenumset

store different enum types in enumSet

I want to store different enum types within one enum.

Is this the right (shortest) way?

public enum MyEnums {
    all(EnumSet.of(Color.red, Shape.round));

    MyEnums(EnumSet<? extends Enum<?>> keys) {
        this.keys = keys;
    }

    private final Set<? extends Enum<?>> keys;

    public Set<? extends Enum<?>> getKeys() {
        return keys;
    }
}
Solution

  • Use a different kind of set. EnumSet is designed to hold enum values of a single kind only:

    All of the elements in an enum set must come from a single enum type

    The point is that it is very efficient because it stores a bit mask of the present ordinal values - most enums have fewer than 64 values, so all it basically needs in terms of member variables is the Class and a long. (There is a private subclass of EnumSet called something like JumboEnumSet which handles larger enums).

    If you have multiple enum types, it can't distinguish values from different enums with the same ordinal.