ThreadLocal with Supplier for static fields

Question

I have a bunch of static utility fields and I am wondering if I should use ThreadLocal for all of these fields.

version 1 (with ThreadLocal Supplier):

private static final ThreadLocal<DateTimeFormatter> TIME_FORMAT = 
ThreadLocal.withInitial(() -> DateTimeFormatter.ofPattern("HH:mm:ss"));

version 2 (normal):

private static final DateTimeFormatter TIME_FORMAT_2
 = DateTimeFormatter.ofPattern("HH:mm:ss");

What are the consequences, benefits, pitfalls when using version 1 instead of version 2. Which one should I prefer and why (memory, performance)?

Answer 1

ThreadLocal is used to have different instances for different threads.
Since DateTimeFormatter is thread safe, there is no advantage of version 1.
Use version 2.

Answer 2

Even if is thread safe, there could be an advantage in general, because with a ThreadLocal you can imitate a cache , so within the thread the instance is only created once and not for every call.

So I think the memory, performance will be better when using ThreadLocal . The DateTimeFormatter is only an example here to illustrate the general useness of a ThreadLocal but it could also be a regular expression (coming from Pattern.compile() ) or anything else which may be useful for caching.