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From Ceki Gülcü <c...@qos.ch>
Subject Re: Differences in XMLConfiguration beetween ver. 1.1 and 1.2
Date Thu, 30 May 2002 16:07:23 GMT


If MyLogger introduces a new method that your code uses, then your
code is tied to MyLogger.  It is *expecting* to use a MyLogger
instance. Your code won't work with any other Logger class.

At the same time, when you write

   Logger l = Logger.getLogger()

you don't actually know the type that is returned. It may well be an
instance of EnhancedLogger with a totally different logging
behavior. You just don't know and don't have to care as long as you
strictly adhere to the methods available in the Logger class.

At 17:41 30.05.2002 +0200, Giuseppe Madonna wrote:

> > >However I wonder, to avoid Logger subclassing, why not make it final?
> > >But it was just a thought...
> >
> > Logger class is not final because Logger sub-classing allows very
> > important enhancements such as security or transparent logging domains.
> > Domains are a "secret" feature planned for log4j 1.3.
> >
> > The important point to note is that these sub-classes do not change
> > the Logger interface, that is the set of methods available to the
> > user.  Sub-classing Logger by adding new logging methods is strongly
> > discouraged because code written for such loggers will simply not run
> > in environments where the enhanced Logger sub-classes are used. (I am
> > thinking of Application Servers and Servlet Containers.)
> >
> > Does it make any sense?
>
>I'm missing the point.
>Code will run fine anyway.
>This is java, not C++ and (dynamic) linking is done at runtime, not at
>compiletime.
>If I extend from Logger class, e.g. MyLogger, code referring to MyLogger
>methods will run fine
>with log4j 1.999 version in which there will be a EnanchedLogger class
>extending from Logger.
>If you want to preserve public interface, you can (must) use java Interface
>concept.
>If you want to make new improvements and make it available to users, you can
>(must) extend your old interface.
>Application written for old interface are preserved and will runs fine:
>backward compatibility is granted.
>Who wants to use new enanchements will refer to new Interface.
>
>Best regards,
>Giuseppe.
>
>
>
>
>
>
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Ceki

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