java - Calculate second between my data and current data -

how can calcutate second between currenttime , date?

long time = mydata - systemclock.elapsedrealtime(); 

you use system.currenttimemillis() current. use system.currenttimemillis() again on time of offset. use latest 1 , subtract first one.

systemclock.elapsedrealtime(); returns time since bootup. not speific time.