public static void awardBonusInternal() {
        BigInteger bonusReduction = BigInteger.valueOf(100);

        christmasBank.getAllAccounts().parallelStream().
                filter(account -> account.getBalance().signum() > 0).
                forEach(account -> account.deposit(account.getBalance().divide(bonusReduction)));

        System.out.print("Balances of all accounts (int): ");
        for (BankAccount account: christmasBank.getAllAccounts())
            System.out.print(" " + account.getBalance());
        System.out.println();

    }