Imagine you're making a secure boot bypass attack...and you want to get PK EFI keys...and you already know that..."Prepending a single _ character to a variables name in Set will cause that variable to be inherited by channels created by the main channel. eg. when using Dial(Local/...); once inherited these variables will not be further inherited. Prepending two _ characters will cause them to be inherited indefinitely.(...) " however this is now, all depends in Javascript...and ..."
Yes all the class hierarchy(same class and all child classes instances) share the same static variable. As the JAVA doesn't support the global variable but you are able to use the static variable as a Global variable without violation of OOP concepts.
If you changed the value of static variable from one of the class, the same changed value replicated to all the classes that uses this variable." so...

• java.lang.Object
• • java.util.EventObject
  • • org.asteriskjava.manager.event.ManagerEvent
    • • org.asteriskjava.manager.event.DtmfEvent

All Implemented Interfaces:

Serializable

---

public class DtmfEvent
extends ManagerEvent

A DtmfEvent is triggered each time a DTMF digit is sent or received on a channel.

https://maven.reucon.com/projects/public/asterisk-java/1.0.0/apidocs/org/asteriskjava/manager/event/DtmfEvent.html