Enum default methods

Question

I'm trying to add a default method for some of my enums using an interface with default method. The method should check if enum is in array(varargs) of enum values.

First warning I get is "Possible heap pollution from parameterized vararg type", but it's not in case of enum, cause it's final, right?
Second warning is "Unchecked cast: BaseEnum<E> to E" (and "Suspicious call" warning witout cast). It also would be safe until I pass right type parameter when implementing my interface. Here is my example code:

public interface BaseEnum<E extends Enum<E>> {

    @SuppressWarnings("unchecked")
    default boolean in(E ... statuses){
        return Arrays.asList(statuses)
                .contains((E) this);
    }
}

public enum Transport implements BaseEnum<Transport> {
    CAR, BUS, PLANE
}

public enum Fruit implements BaseEnum<Fruit> {
    APPLE, CHERRY, LEMON
}

With this implementations everything looks safe. But how can I prevent something like this?(By 'prevent' I mean some code restrictions)

public enum Transport implements BaseEnum<Fruit> {
    CAR, BUS, PLANE
}

I've looked at new Java 15 sealed feature, but seems its not the case. Is there any cleaner solution?

It's not possible

Michael
– Michael

2021-06-07 18:20:56 +00:00
Commented Jun 7, 2021 at 18:20 — Michael
– Michael, Commented Jun 7, 2021 at 18:20

M A · Accepted Answer · 2021-06-07 19:03:12Z

6

There is no need to create an interface for such an operation. The EnumSet class serves this purpose:

Fruit fruit = ...;
boolean match = EnumSet.of(Fruit.APPLE, Fruit.CHERRY).contains(fruit);

answered Jun 7, 2021 at 19:03

M A

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3 Comments

Andrei Yusupau Over a year ago

Thanks for your reply. But when I compare this approaches, second looks clearer: 1) boolean match = EnumSet.of(Fruit.APPLE, Fruit.CHERRY).contains(fruit); 2) boolean match = fruit.in(Fruit.APPLE, Fruit.CHERRY);

M A Over a year ago

@AndreiYusupau I don't think you can make it type safe using your approach. Your interface may be implemented by a regular class rather than an enum. One thing to note is that you don't really need the cast in the contains() method, you can just do .contains(this);.

Andrei Yusupau Over a year ago

If it happens so that this won't be of type T without cast it would just silently return false, but with cast it would be an ClassCastException.

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