Question

I have the following question.

Assume we have third party software that send us transaction (atm cards) information in following style:

atm card 4**5048 debited 42$. 231$ Left.

So, I have debited sum, sum left and card no in each transaction.

So I create class

class Transaction {
    private String mCardNo;
    private Double mAmount; // Actually. I dont store money as double, but let it be:)
    private Double mSumLeft;
}

One day second software appears and starts to send the info:

atm card 4**5048 debited 42$: purchase at Apple Store. 231$ Left.

And I think that its awesome to have info about place, where user made a purchase.
There are two options: extend Transaction class or add a new attribute “place”.

One day new software is added and now I have to support 3 types of message!

atm card Visa Classic 4**5048 debited 42$: purchase at Apple Store. 231$ Left.

Oh, God! and Im pretty sure that it will be more than 100 types of messages containing unique numbers of attributes (because I have about 50 now!)

So what is the best way to store additional attributes?

Answer 1

If there’s so much variability in the number of attributes, maybe you should store them in a single class (to avoid an explosion of subclasses) as values in a series of Map attributes and identify them with a String key (say, Map<String, Double>, Map<String, Integer>, etc.)