What will happen if you start a service with out any thread, that does heavy functionality?
i. Nothing will happen, it runs finely.
ii. May lead to ANR (application not responding) error some times.
iii. option 2 is right, but that is applicable if your application is having at least one activity, since that activity will run in UI thread.
iv. option 2 is right, whether you have at least one activity or not in your application.