class Reise { ... }

class HashListe implements Iterable<Reise> {
    void settInn (Reise r) { ... }
}

class Filter {
    Reise filtrer (Reise r) {
	if ( ?r er OK? ) return r;
	else return null;
    }
}

class Monitor {
    HashListe data = new HashListe();
    Lock laas = ReentrantLock();

    void settInn (Reise r) {
	laas.lock();
	try {
	    data.settInn(r);
	} finally {
	    laas.unlock();
	}
    }
}

class MonitorDemo {
    public static void main (String[] arg) {
	HashListe[] mangeReiser;
	: ?Fyller mangeReiser?
	Monitor mon = new Monitor();
	Filter f = new Filter();
	CountDownLatch barriere = new CountDownLatch(mangeReiser.length);

	class ParaFilter implements Runnable {
	    HashListe mineReiser;

	    ParaFilter (HashListe lst) {
		mineReiser = lst;
	    }

	    @Override
	    public void run () {
		for (Reise r: mineReiser) {
		    Reise rx = f.filter(r);
		    if (rx != null)
			mon.leggTil(rx);
		}
		barriere.countDown();
	    }
	}

	for (int i = 0;  i < mangeReiser.lenght;  ++i) {
	    ParaFilter pf = new ParaFilter(mangeReiser[i]);
	    new Thread(pf).start();
	}

	try {
	    barriere.await();
	} catch (InterruptedExpression e) {}

	for (Reise r: mon.data) { ... }
    }
}