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List:       velocity-user
Subject:    Re: ResourceLoader.init() question
From:       James Maes <jmaes () sportingnews ! com>
Date:       2002-01-06 6:30:17
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#define ckeleton skeleton
#define programer programmer


okay, I'm done....

On Sunday 06 January 2002 12:27 am, James Maes wrote:
> Class Behavioral - Template Method
> Intent - "Define the ckeleton of an algorithm in an operation, deferring
> some steps to subclasses.  Templates Method lets subclassess redefine
> certain steps of an algorithm without changing the algorithm's structure."
>
> - James "Bored programer with a copy of Design Patterns in front of me"
> Maes
>
> On Sunday 06 January 2002 12:13 am, Donnie Hale wrote:
> > The "template method pattern" doesn't have anything to do with
> > "templates" as in C++ or "generics" as in JDK 1.4/5. It's the name of a
> > pattern from the "Gang of 4" Design Patterns book. I don't have my copy
> > in front of me right now to provide the "official" motivation and
> > application of the pattern, but, in short, it establishes a non-virtual
> > public interface through a base class whose implementation is a
> > "template" which can/must be overridden by derived classes.
> >
> > As far as protected member variables in a base class goes, Geir's last
> > message summed it up most concisely: it violates encapsulation.
> >
> > While the books aren't Java-specific, the rules in Scott Meyers'
> > "Effective C++" and "More Effective C++" are highly applicable.
> >
> > Donnie
> >
> > > -----Original Message-----
> > > From: Nick Bauman [mailto:nick@cortexity.com]
> > > Sent: Saturday, January 05, 2002 10:38 PM
> > > To: velocity-user@jakarta.apache.org
> > > Subject: RE: ResourceLoader.init() question
> > >
> > >
> > > Donnie said:
> > >
> > > [edit]
> > >
> > > > If one subscribes to the Liskov substitution principal (a derived
> > > > class should be able to be used wherever a base class is used w/o the
> > > > user having to know which it is), then more up-front attention needs
> > > > paid on two fronts: 1) what is the full contract of a base class? 2)
> > > > does a derived class really meet the "is-a" test?
> > > >
> > > > I'm a huge fan of the template method pattern, and I think it's wider
> > > > use in base classes would help enormously. As regards this question,
> > > > it would help because the base class would be enforcing the state
> > > > machine, if you will, through which its implementation progresses. It
> > > > could then very easily pass what might otherwise be a protected
> > > > member variable to an abstract template method for derived class use.
> > >
> > > Templates aside for a moment and I generally agree (because I think
> > > they're good too), this is Java: we use interfaces to establish
> > > contracts.
> > > Liskov substitution principal is what the Java interface is all about.
> > > Without interfaces, implementations end up pushing more and more
> > > functionality up the heirarchy tree into what become abstract God
> > > classes.
> > > Yeech. While it's true that "nobody looks at what's in the base classes
> > > enough" (how many times have I seen people rewrite stuff that's
> > > already in
> > > the base class they weren't paying attention to!), this doesn't
> > > negate the
> > > value of protected members. Again, Templates aside, sometimes things
> > > are simply correctly factored by using protected member variables in a
> > > base class.
> > >
> > > --
> > > Nick Bauman
> > > Cortexity Development
> > > http://www.cortexity.com/
> > >
> > >
> > > --
> > > To unsubscribe, e-mail:
> > > <mailto:velocity-user-unsubscribe@jakarta.apache.org>
> > > For additional commands, e-mail:
> > > <mailto:velocity-user-help@jakarta.apache.org>

-- 
 
------------------------------------
|| James Maes        
|| Senior Programmer 
|| jmaes@sportingnews.com 
|| The Sporting News     
|| www.sportingnews.com 
------------------------------------

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