This page describes the experimental javadt tool:
  http://docs.oracle.com/javase/8/docs/technotes/guides/jpda/javadt.html

AFAIK, this tool was in the standalone JPDA download but was never included in the JDK.


This page describes has incorrect instructions on how to run jdb and has instructions for building jdb that date back to when JPDA was a separate download.

  http://docs.oracle.com/javase/8/docs/technotes/guides/jpda/jdb.html

It may be that the jdb page can be removed.