Hi,
The lifecycle of a B4J application is different than that from a B4A application.
On Android the OS can easily kill processes when the OS decides it is needed. For Java applications (created by B4J) once an application is started the OS will not kill it by itself, so you can rest assured that when an application is started it will keep running until it is killed explicitly.
I don't think B4J can create "service" applications (as in Windows services) as such type of applications do not exist on other OS's (Linux for example): in Linux for example you can just start an application as a cronjob (or @reboot).