How to work with time in Java?

Question

Java

I'm a newbie and this problem is confusing me.
By pressing the button, the chronometer starts working, showing how much time has passed since pressing (up to months and years). Initially, I just worked with a variable that increased every second, I realized that it was not an option, because when the application is closed or the phone is rebooted, the time counter is reset. Please help and advice on how to implement this idea

Answer 1

Just store the button click date in a database or a file.
For java 8+ use: LocalDateTime
For earlier versions : Date