Periodisches Ereignis

 Runnable helloRunnable = new Runnable() {
    public void run() {
        System.out.println("Hello world");
    }
};

ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
executor.scheduleAtFixedRate(helloRunnable, 10, 10, TimeUnit.SECONDS);

long oldTime=System.currentTimeMillis();
float delTime=0;
float countDown=100;
run(){
while(countDown>=0)//vllt noch eine zweite abbruchbedingung die du von aussen steuern kannst um die schleife abzubrechen
{
    deltime=(float)(System.currentTimeMillis()-oldTime);//dieser cast ist okay

    if(deltime>=1000)
    {
        oldTime=System.currentTimeMillis();
        countDown-=delTime/1000f;//rechnung: millisekunden genau
        if(countDown<=0)
            System.out.println("BOOOOOOOOM");//booom countdown abgelaufen-alle tot
        else
            System.out.println("Countdown:  "+(int)countDown+" sek")//ausgabe:"Countdown: 89 sek" z.B./ausgabe: sekundengenau
    }
    else try
           {
                this.sleep(250);
           }
           catch(InterruptedException e)
           {
                 //Weltkrieg einleiten
           }
}
}

 public class TimerDemo {    public static void main(String[] args) {       // creating timer task, timer       TimerTask tasknew = new TimerScheduleFixedRateDelay();       Timer timer = new Timer();              // scheduling the task at fixed rate delay       timer.scheduleAtFixedRate(tasknew,500,1000);          }    // this method performs the task    public void run() {       System.out.println("working at fixed rate delay");          }     }

getActivity().runOnUiThread( new Runnable() {
  public void run() {
     ... TextView ändern ...
  }
});