Re: coarse-grained object and fine-grain object
On Tue, 7 Sep 2010, markspace wrote:
On 9/7/2010 3:58 PM, Tom Anderson wrote:
Perhaps coarseness of grain isn't about what the objects are, but what
you *do* with them - whether you lock one at a time, or hundreds;
whether you allow access to one at a time, or hundreds; whether you
send one at a time over the network, or hundreds. Maybe the objects are
the ruler with which you measure the grain.
My understanding (and I could be wrong about this) is the grain is about
designs and interfaces, not objects per se. Of course, objects
implement the design, so you do have objects eventually, but it's more
about the intent and the way objects are used.
Aha.
Here's a coarse grained interface for an HTTP Request:
public interface HttpRequest {
OutputStream handleRequest( Request r )
throws HttpException;
}
That's it.
Instinctively, i agree. And i think i can fit this into my theory: there
may be small objects in the request, but the operation we're looking at
here deals with them en bloc, taking a large aggregate of objects, the
Request, and producing a large output, in the form of a load of bytes.
There's really only one way to use this API. It does everything you
want, is almost impossible to configure incorrectly (there's no
configuration!) and high level code way up in the design hierarchy will
have no problem using this because there's only one way to use it. No
matter what happens, it's very unlikely that changes to the
implementation will affect the way that high level code uses this
interface because it is so simple. This is an advantage for interfaces
that are designed to be extended and then used by library code or
frameworks or applications like JEE containers, since it's easy to
predict what the user is going to do and handle all possibilities
correctly.
Now fine grained APIs would be more like Swing, where you have a configure
this and a configure that for every conceivable option. And sometimes Swing
does interact weirdly with its sub-components because, well, there's a lot of
ways those components can be used and it's not always clear how they do
interact.
That's very interesting. That's a whole angle i hadn't thought about.
Coarse grain as a kind of simplicity, which gives robustness.
tom
--
If you're going to print crazy, ridiculous things, you might as well
make them extra crazy. -- Mark Rein