public GiroKonto erzeuge_giro_konto(String accountNumber, long creditLimit) throws BankException, RemoteException {
Konto konto = finde(accountNumber);
if(konto != null)
throw new BankException("account already exists!");
GiroKonto giroKonto = new GiroKontoImpl(accountNumber, creditLimit);
kontos.put(accountNumber, giroKonto);
return giroKonto;
}