Re: Ensuring a method is overridden

From:

Robert Klemme <shortcutter@googlemail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 08 Sep 2009 22:42:31 +0200

Message-ID:

<7gntueF2qhe9iU2@mid.individual.net>

On 08.09.2009 08:40, Lew wrote:

Roedy Green wrote:

On Mon, 07 Sep 2009 23:20:32 -0500, Mike Amling <mamling@rmcis.com>
wrote, quoted or indirectly quoted someone who said :

A certain class is used 80% of the time as is, and is extended 20%
of the time. I want to ensure that each subclass overrides a certain
method. The only way I can think of to do this is to put code in the
base class's constructors, and when the class being constructed is
not the base class, check that getDeclaredMethod does not throw a
NoSuchMethodException.
Does anyone know of a more efficient way? At compile time, maybe?

The other way out of this is to put an assert in the method that must
be overridden.

It could use this.class to figure out if it is working with a base
class or an extension. If they have overridden, the assertion won't be
there.
To get fancy you want to make it ok if they call super. You could look
at the stack. See http://mindprod.com/jgloss/trace.html

Others might have better ways of doing this with a run time check.

Since the 'abstract' keyword works, and reflection is both messy and
slow, eschew reflection.

Also, asserts are (and should be) OFF most of the time.

Any time you code an instance to figure out what class it is in order to
decide which behavior to use, you've messed up. (To nitpickers: that's
the first order of approximation.)

(and the second)

(...)

You don't need a run-time check.

Right.

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/