How to run a method every X seconds

The solution you will use really depends on how long you need to wait between each execution of your function.

If you are waiting for longer than 10 minutes, I would suggest using AlarmManager.

// Some time when you want to run
Date when = new Date(System.currentTimeMillis());

try {
    Intent someIntent = new Intent(someContext, MyReceiver.class); // intent to be launched

    // Note: this could be getActivity if you want to launch an activity
    PendingIntent pendingIntent = PendingIntent.getBroadcast(
        context,
        0, // id (optional)
        someIntent, // intent to launch
        PendingIntent.FLAG_CANCEL_CURRENT // PendingIntent flag
    );

    AlarmManager alarms = (AlarmManager) context.getSystemService(
        Context.ALARM_SERVICE
    );

    alarms.setRepeating(
        AlarmManager.RTC_WAKEUP,
        when.getTime(),
        AlarmManager.INTERVAL_FIFTEEN_MINUTES,
        pendingIntent
    );
} catch(Exception e) {
    e.printStackTrace();
}

Once you have broadcasted the above Intent, you can receive your Intent by implementing a BroadcastReceiver. Note that this will need to be registered either in your application manifest or via the context.registerReceiver(receiver, intentFilter); method. For more information on BroadcastReceiver‘s please refer to the official documentation..

public class MyReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent)
    {
        System.out.println("MyReceiver: here!") // Do your work here
    }
}

If you are waiting for shorter than 10 minutes then I would suggest using a Handler.

final Handler handler = new Handler();
final int delay = 1000; // 1000 milliseconds == 1 second

handler.postDelayed(new Runnable() {
    public void run() {
        System.out.println("myHandler: here!"); // Do your work here
        handler.postDelayed(this, delay);
    }
}, delay);