public static void checkAllPositives(String customerId) {
        // External iteration
        boolean allPositives = true;
        for (BankAccount account: christmasBank.getAllAccounts())
            if ( account.getCustomerId().equals(customerId) && (account.getBalance().signum() < 0) )  {
                allPositives = false;
                break;
            }
        System.out.println("All positive balances for " + customerId + " (ext) is " + allPositives);
        //Internal iteration
        boolean allPositivesAlt = true;
                // To be worked out.
        System.out.println("All positive balances for " + customerId + " (int) is " + allPositivesAlt);
    }