Nothing in JUMG has a private modifier - although it's bad practice - but as far as this library is concerned, there is no need to privatize anything.
A good way to incur users hate on you...
... as soon as you change implementation details - what will happen sooner or later.
Exposing each and every member means extending the public interface that a library offers its user base.
And changing internal details will break people's code quite probably.
A special problem occurs when on the one hand synchronizing stuff for thread safety but at the same time making locked members public.