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Posted to dev@poi.apache.org by bu...@apache.org on 2008/10/02 07:26:28 UTC

DO NOT REPLY [Bug 45919] [PATCH] Crucial classes made inheritable: HSSFWorkbook, HSSFSheet, HSSFRow and HSSFCell

https://issues.apache.org/bugzilla/show_bug.cgi?id=45919


Josh Micich <jo...@gildedtree.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX




--- Comment #6 from Josh Micich <jo...@gildedtree.com>  2008-10-01 22:26:27 PST ---
>From a functionality perspective, you are probably tryng to do something very
sensible.  Can you please attach some sample code that shows your goal?

However, the technical change specified in these patches is contrary POI's
current direction.  POI avoids allowing API classes to be extended because of
the difficulties that this presents.  The trouble arises because inheritance is
such an intimate form of coupling.  

The most discernible difficulty relates to maintaining of backward
(source/binary) compatibility.  This link has some useful tables classifying
potential changes:
http://wiki.eclipse.org/index.php/Evolving_Java-based_APIs

Much more subtle are the unexpected behaviour/logic consequences of
inheritance.  See this page for some well explained examples:
http://norvig.com/java-iaq.html

Most code using unwanted inheritance can be rewritten using delegation and/or
the 'strategy pattern'.

Don't get me wrong - inheritance isn't all bad.  POI uses *plenty* of
inheritance, just internally. My personal opinion is that "you should never
inherit from a class that you do not control the source code of".


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