Why is one of the singletons not synchronized?

Question

Java

Hi everybody.
In one of the Google projects there are two singletons: the first one is for working with local storage, the second one is for working with remote storage.
The question is, why does one singleton have a synchronized block and the other doesn't?

Answer 1

the first is thread-safe, the second is not
about singletons https://habr.com/en/post/27108/
both are worse than On Demand Holder