We have two fields in DCmdFactory, _enabled and _hidden:

============
class DCmdFactory: public CHeapObj<mtInternal> {
  // When disabled, a diagnostic command cannot be executed. Any attempt to
  // execute it will result in the printing of the disabled message without
  // instantiating the command.
  const bool _enabled;
  // When hidden, a diagnostic command doesn't appear in the list of commands
  // provided by the 'help' command.
  const bool _hidden;
============

All DCmdFactory are currently constructed with _enabled set to true. This seems to be a relic that no longer serves any purpose.

_hidden is currently also always set to true, although it may be useful in the future. E.g., if we are deprecating a dcmd, we can hide it from the list but still leave it enabled for compatibility. Example:

https://github.com/openjdk/jdk/blame/401d0d6b09ea422eacecda2900793a416097dc9b/src/hotspot/share/services/diagnosticCommand.cpp#L165C59-L165C59

(The above line was eventually removed in JDK-8336401).