Peter,
Before we get into an argument of TASTE, what do you want to accomplish
with your idea of interface, which you can't do with the PageFactory and
subclassing?
Adding Spring annotations? What kind of annotations do you want to add?
What kind of functionality do you wish to do? Does it /have/ to be done
'the Spring' way, or might there be another way to accomplish what you want?
Martijn
Peter Veentjer - Anchor Men wrote:
And that is a /GOOD/ thing. Most methods are an implementation detail,
that need to be called in the framework. As Eelco and Johan and others
already said here: the Component hierarchy has very particular behaviour
that needs to be fixated at several places in the framework in order to
remove the possibility of 'clients' altering that behaviour.
______________________________________
I don`t have problems with final methods. If a method was not designed to be overwritten, make it final. But I have problems if I can provide an alternative implementation that obays a general contract.
No, subclassing /used/ to be overrated. Subclassing has its place in an
O.O. design. Look at the design patterns of Gamma et al. they use
inheritence quite to the fullest and no one is calling their designs the
sign of a beginning O.O. developer!
______________________________________
You didn`t get my point. I didn`t say all subclassing is bad, just a lot of it.
There are a lot of ways to add functionality and subclassing is one of them. In
most cases (not all) there are better ways that give a more flexible design. A
lot of patterns in the GoF book are based on that assumption. and not on 'just'
subclassing.
Talking about a knee jerk reaction! The main architect of Wicket has
over 20 years of O.O. design and development experience, he has worked
on the Swing/JFC team and is considered by his peers as top notch.
Hardly a beginning O.O. developer.
______________________________________
Maybe.. but you can`t tell my Swing is written extremely well. Check out all
the AWT-Garbage. In general the Swing API is workable, but it could have been a
lot better and cleaner.
And I guess there is not a 'best' way to write software, but using class where interfaces should have been used is not the way I like to write software. Check out other api`s, like the collectionframework/concurrency framework/Spring. Most things are based on interfaces. Imho everything that defines a type and is 'core' (used by a lot of developers with a lot of different needs) should be designed from an interface.
Just my two cents...
-Matej
Another reason not to use interfaces here is that there is so much
behaviour in here (in the pages and components), that it is very hard to
extract something usefull out of it. What would the interface of a Page
be? One of the good practices when making interfaces is that they should
be small. Having an interface like
http://jakarta.apache.org/tapestry/tapestry/apidocs/org/apache/tapestry/IPage.html
doesn't really display that. They can be large, like the collection
interfaces are, but they have to be really, really stable and consistent.
Just to be sure, and as I didn't make this decision for Wicket I asked
Jonathan Locke (who is doing movie stuff now, and left the mailing lists
for some time) why he choose for interfaces. Here's a partial transcript
of our chat:
[22:31] jonathan: i don't believe in big interfaces
[22:31] jonathan: no interface should be as large as Page
[22:32] jonathan: it's too fragile
[22:35] jonathan: abstract classes are evolvable
[22:36] jonathan: interfaces should always be a set of methods that you
cannot ever imagine extending
[22:36] jonathan: it encapsulates a very specific set of behaviors
[22:37] jonathan: everyone should feel free to create/extract his own
IPage interface for use with proxies
[22:38] jonathan: there's something fundamentally wrong with the way
that current OO languages try to wire things together with static
interfaces.
[22:39] jonathan: unless i'm missing something, this is really not a
problem with wicket
[22:40] jonathan: in fact i think it's a feature
[22:40] jonathan: interfaces are really most useful for things that are
truly pluggable
[22:43] jonathan: my ideal number of methods in an interface is 1
[22:43] jonathan: ;-)
[22:44] jonathan: 2 is okay in some cases
[22:44] jonathan: 3 often should be re-thought
[22:44] jonathan: the more methods you have, the more likely it is that
you've got a bad design
So, it is a design decission not to work with interfaces. However, as
Jonathan stated, you could extract an interface, let your page class
implement it and off you go. Furthermore, I wonder what it is you want
to do with a proxy that you can't do by simply subclassing? Or AOP?
As a final statement I'd like to add that a framework like Wicket is
very different from a business system, which could have tons of business
methods that must be pluggable. Though even in that case, I think too
that interfaces are overused/ get too much focus with some of the
current popular frameworks. Seems to be getting a knee-jerk reaction
instead of a design decision. But maybe that's just me.
Regards,
Eelco
Peter Veentjer - Anchor Men wrote:
I`m trying to add Spring annotations to the Page, but because there is
no page interface and only a Page class (with final methods) it is not
possible to create a proxy and therefor it is impossible to enhance
objects. This is very inconvenient..
Why are the components not designed from interfaces? Designing from
interfaces is common oo practice.
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