public void update(Activity activity) throws InstanceNotFoundException {
		boolean found = false;
		Iterator<Activity> iter;
		iter = activities.iterator();
		while (iter.hasNext() && !found) {
			Activity a = iter.next();
			if (a.equals(activity)) {
				found = true;
				a.setPlaces(activity.getPlaces());
				a.setPrize(activity.getPrize());
				a.setStudents(activity.getStudents());
				Persistence.getInstance().save();
			}
		}
		if (!found) {
			throw new InstanceNotFoundException(activity, "Activity");
		}
	}