Comment by nmadden

Yes, in theory they are good. In practice they cause enormous amounts of pain and work for library maintainers with little benefit to them (often only downsides). So, many libraries don’t support them and they are very hard to adopt incrementally. I tried to convert a library I maintain to be a module and it was weeks of work which I then gave up and reverted. As one library author said to me “JPMS is for the JDK itself, ignore it in user code”.

Given how much of a coach and horses modules drove through backwards compatibility it also kind of gives the lie to the idea that that explains why so many other language features are so poorly designed.