Re: When would you use abstract classes over interfaces

From:
Tom Anderson <twic@urchin.earth.li>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 30 Jul 2008 18:22:13 +0100
Message-ID:
<Pine.LNX.4.64.0807301821160.17886@urchin.earth.li>
On Wed, 30 Jul 2008, Lew wrote:

Andy Dingley wrote:

On 29 Jul, 02:56, Lew <com.lewscanon@lew> wrote:

An abstract class
* may have implementation.


So what's an abstract class for? If you want an interface, use an
interface; if you want to attach implementation, consider an abstract
class.

Both of these are viable approaches, but they're not exclusive (as is
too often thought). There's nothing that says "If you want an
interface with a bit of implementation too, then use an abstract class
_instead_of_ an interface".

If you are in this case, consider using _both_ instead. Define the
interface with an interface (that's what they're good for) and then
write an abstract class that implements this interface and attaches
the implementation that you need.


This approach is good, because it takes into account that an abstract
class is the root of a singly-rooted hierarchy.


It's also potentially overengineering, though. If you don't need the
flexibility that this pattern gives you, just use an abstract class. If
you later find that you do need it, refactor. Doing this right from the
outset makes my YAGNI sense tingle.

tom

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