@Override
    public Double deposit(String id, Double in) {
        if(id == null || "".equals(id.trim()) || in < 0) {
            return -1.0;
        }
        for(Account a : accounts) {
            if(id.equals(a.getId())) {
                a.setBalance(a.getBalance()+in);
                System.out.println("Deposited " + in + " RMB successfully.");
                return a.getBalance();
            }
        }
        return -1.0;
    }