When you connect to a database from the debugger, the Connection window shows all currently active Java VMs under the user login name. If there are none, the debugger goes into wait mode. Wait mode works like this:
Each time a new Java VM is started, it shows up in the list.
You may choose either to debug the new Java VM or to wait for another one to appear.
Once you have passed on a Java VM, you lose your chance to debug that Java VM. If you then decide to attach to the passed Java VM, you must disconnect from the database and reconnect. At this time, the Java VM appears as active, and you can attach to it.