Notice how this uses a sun.* package, i.e. a hidden implementation detail of 1 specific JVM . Java was never guaranteed to have it in the first place. Some of

Notice how this uses a sun.* package, i.e. a hidden implementation detail of 1 specific JVM . Java was never guaranteed to have it in the first place. Some of these classes were so usefull that people used them even if they shouldn't. There are compatibility flags in the jvmbto allow access even in java 9, but each new version slowly causes additional pain. One risk of using libraries (or working with other people) is that you don't know if they limited them selves to good enough practices. Most do, a small percentage doesn't, but they cause pain for all of us.