what is wrong with my code ?

    public class AccumulateSavingsBatch {
    private Bank bank;
    public void setBank(Bank bank)
    {
        this.bank=bank;
    }
    public void doBatch()
    {
        for (Customer c : bank)
        {
            for (Account a : c)
            {
                if(a instanceof SavingAccount)
                {
                    a.accumulateIntersest();
                }
            }
        }
    }
}