android - Can't remove TITLE BAR -

i know question has been asked million times. none of answers helped me.
every time want remove title bar on mainactivity extends actionbaractivity, application crashes or nothing happens. have tried - changed androidmanifest settings, added:

requestwindowfeature(window.feature_no_title); 

and

supportrequestwindowfeature(window.feature_no_title); getwindow().setflags(windowmanager.layoutparams.flag_fullscreen,                           windowmanager.layoutparams.flag_fullscreen); 

in possible way oncreate method. nothing seems work properly. hope has answer because getting frustrating.

don't extend actionbaractivity causing error, instead use activity. unless min api level not below 11, won't change (here can read why, appcompatactivity cause same error).
if extends activity, can use getwindow().getdecorview().setsystemuivisibility(view.system_ui_flag_fullscreen) (min api lvl 15).