Check out example codes for "android timer". It will help you in understanding the concepts better.
Code Example 1
private int counter;
TimerTask timerTask = new TimerTask() {
@Override
public void run() {
Log.e("TimerTask", String.valueOf(counter));
counter++;
}
};
Timer timer = new Timer();
timer.schedule(timerTask, 0, 1000);
Learn ReactJs, React Native from akashmittal.com