public void addTown(Town town) throws AlreadyRegisteredException {
if (hasTown(town)) throw new AlreadyRegisteredException();
else {
towns.add(town);
town.setWorld(this);
}
}
public void removeTown(Town town) throws NotRegisteredException {
if (!hasTown(town)) throw new NotRegisteredException();
else {
towns.remove(town);
try {
town.setWorld(null);
} catch (AlreadyRegisteredException e) {
}
}
}