Enum values() method efficiency

Question

Is there any inefficiency in calling the values() function of a specific enum class multiple times?

I have seen instances of existing code where the results of values() are cached for reuse. Is this useful?

public enum Blah {

    private static final Blah [] _myValues = values()

    ...

    public static Blah findBlahFromName(String name) {
        for (Blah blah : _myValues) {
            ...
        }
    }

}

Answer 1

It's a good idea to cache the result of values() inside the enum itself if you use it multiple times. That's because, every time you invoke values() method, it creates a new array. So, that is really not required, as you are always going to get the same array elements.

As noted in comments, sharing a cached array will not be thread safe, as other thread can modify the indices in the array, as it's mutable. An option is to wrap the elements in a List<YourEnum> , and share the list using Collections.unmodifiableList() .

Answer 2

Yes, it is inefficient, but there's another way to do it that's not nearly as expensive:

EnumSet.allOf(MyEnum.class);

EnumSet has special wiring into the JDK to allow it to reuse the underlying array.