Whats the best way to initialize classes in the activity lifecycle

Hello,
I come from a Desktop background and I think my approach with my android app reflects that.
My App basically consists of one Mainactivity which holds amongst other things a tcp and bluetooth member. The problem is that every time the activity is recreated the members are reset and everything will be restarted. Is there a way to keep my tcp and bluetooth instances through the lifetime of my app and not my activity.