ArrayList，信用卡总结

Question

我有大部分代码用于阻止信用卡持有人的数量，对于某种卡类型，余额和平均值，由于某种原因，某些内容无效。我在Java，bluejay工作，如果这是一个区别。代码如下，

public String getCardSummary(String card){
    //return a String that summarizes the total number of cards and average debt for the requested card type.
    //Valide enters are: Discover, Visa, and MasterCard. 
    //Return an appropriate error message if the card is not valid.
    //If there are no customers with the specific card, return a message indicationg that "Customers was not found"
    //User the NumberFormat class to help fromat the dollars and cnets outputs. 
    //Sample result should look like:
    //Discover: 1981 cards with average balce of $3,735.20
    if(card.equalsIgnoreCase("Disvoer") || card.equalsIgnoreCase("Visa") || card.equalsIgnoreCase("MasterCard")){
        double runningSum = 0.0;
        int counter = 0;
        for(int i = 0; i < customers.size() - 1; i++){
            if(customers(i).getCard.equals(card)){
                runningSum += custumer(i).getBalance();
                counter ++;
            }
            else{
                System.out.println("Customers were not found.");
            }
        }
        double avg = runningSum / counter;
        System.out.println("" + Card + ": " + counter + " with average balance of " + fmt.format(avg));
    }
    else{
        System.out.println("Invalid Card type");
    }