Comments on: Correcting the Billion Dollar Mistake

By: Peter Lawrey

Peter Lawrey — Tue, 03 Feb 2009 22:03:06 +0000

If you read the news these days, losing a 25 million a year for forty years does sound as much as it used to. 8-/
I prefer fail-fast approaches and not having null could have been worse than what we might have had!

By: Peter Lawrey

Peter Lawrey — Tue, 03 Feb 2009 21:59:24 +0000

I believe JSR-303 suggest @Notnull and @Nullable.
A type which few people consider could be null is enum types. e.g. This can throw an NPE!

switch(myEnum) {
case ENUM1:

IMHO, Variables/fields/parameters should be ‘final’ and not-null by default and only be non-final and/or nullable if explicitly defined so. (Also fields should private by default)

By: Shams Mahmood

Shams Mahmood — Tue, 03 Feb 2009 15:22:16 +0000

@Rickard
I guess we are moving away from the main topic but I’m enjoying this, hence I persist ;). In the case of transfer() the constraints are what is expected of the arguments before transfer() can expect to execute properly. Just like making from non-nullable is a constraint, having from.balance ge amount can be looked upon as a constraint for the caller (deferring responsibility).

By: Kirk

Kirk — Tue, 03 Feb 2009 12:19:27 +0000

Hey, I was there and I do remember it all :)

By: Jevgeni Kabanov

Jevgeni Kabanov — Tue, 03 Feb 2009 10:57:55 +0000

@Kirk
Hey, it was you who was late for the talk, not me. Just ’cause you cannot remember the previous evening doesn’t mean it never happened :P

By: Jevgeni Kabanov

Jevgeni Kabanov — Tue, 03 Feb 2009 10:07:37 +0000

Apparently JSR 308 already includes compiler inference for @Nullable annotation with non-null default:
http://groups.csail.mit.edu/pag/jsr308/

By: Stephan Schmidt

Stephan Schmidt — Tue, 03 Feb 2009 10:06:09 +0000

Yes :-)

By: Jevgeni Kabanov

Jevgeni Kabanov — Tue, 03 Feb 2009 10:03:49 +0000

@Stephan
Nice! I see you’re vouching for the same approach on the 7th slide :)

By: Stephan Schmidt

Stephan Schmidt — Tue, 03 Feb 2009 08:27:29 +0000

BTW Some time ago I held a presentation about

“Better Strategies for Null Handling in Java”

added to SlideShare 5 minutes ago

http://www.slideshare.net/Stephan.Schmidt/better-strategies-for-null-handling-in-java

Stephan

–
Programming is hard – http://blog.codemonkeyism.com
http://twitter.com/codemonkeyism

By: Kirk

Kirk — Tue, 03 Feb 2009 07:24:34 +0000

@Attila, The contract is documented, don’t send me a null and if you do, I’ll send you back an NPE. Throwing an NPE instead of an IAE is maybe not ideal but it does simplify many things. The only confusion that I can see is when you try to sort out if the NPE belongs to me or the framework. Traditionally we, as developers, don’t throw NPE. The question is, why not? What in our thinking limits us or prevents us from throwing this exception? If the contract is clear, don’t pass me a null, the exception conveys the problem very clearly.

Jevgeni, I’m sure it took you more than 30 minutes ‘cos you disappeared after that conversation and I never saw you again. The only way that happens is if you start coding ;-)

Kirk