Re: class hierarchy design problem

"Oliver Wong" <>
Wed, 02 Aug 2006 17:04:17 GMT
"dgront" <> wrote in message

There is my problem

* I have several (say: 5) classes : A, B, C. They rather hold some
data, but sometimes they do some simple operations on theirs data.

* The data can be stored is several various data formats: X, Y, Z, T, U
... Several file formats can store data for a given class. Some file
formats hold more and some less information that is necessary to create
an instance of one of the classes: A B C

* The problem is to feed A, B or C with the data

My current solution:
- Each of the A, B, C classes has reading/writting method for each data
... (and writeTo.. methods)

Unfortunately, many of the formats do not handle all the necessary
data. For instance X has the half of the data and the rest is in Y. But
in the time of constructing object I don't have Y file. It can however
appear in the future.
So in my solution both X and Y readers create A and some of fields are
filled with some 'empty' contents (zeros, spaces, nulls...) If The
second file shows up, A.updateFromY() method is invoked.

In general my program works like that:
A.writeToZ(); // User can stop the program at this point - he will got
a Z file but some fields will be empty
for(;;) // Wait for user action. Also check if Y shows up
A.writeToZ(); // all fields in Z are present

As you can see, creating a method:
does not make sense, usually the two files: X and Y do not come

My solution works not that bad, but:
- there is an explosion of methods: three in each class for each data
format (readFrom, updateFrom, writeTo)

- file format specification is not fixed. Sometimes I face to a file
which my code fails to read. Then I have to trace all methods that
reads that file format in all the classes A, B, C.

- some of the fields of A may be defined both in X and Y. In general
the order:
makes a difference

Can anyone proppose a better solution? There is a bunch of my nevest
- superclass that can read and write all the formats, like,format_X)
is not a good choice for me - I want to keep A, B, C data private.

- at some point I used PostrgeSQL for this purpose. That was great, but
VERY inconvenient. I really need a single standalone program

    You seem to be conflating the concepts of classes and objects, and of
files and file formats.

    What is your program supposed to do? Convert from one file format to

    How about having one stage where you parse all the inputs, and build
model objects out of that. And then a second stage where you walk your model
data structure and emit all the data into files of the appropriate file

    - Oliver

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