I do hope they don't forget DirectBuffer, bug #4724038. This incantation is required to unmap a memory-mapped FileChannel, which you need to do so that you can delete it, because the OS of course locks it:

((sun.nio.ch.DirectBuffer) buf).cleaner().clean();

Apparently they didn't want to make it public because there is no portable way to make it thread safe. Which is just great if you have to work with temporary mmapped files...