Re: is class file backward compatible

Well, it seems to me that with:

So, what will happen if the class, that compiled in the older version of
java complier, has a method that is fully deprecated in the new version
of JVM?

the question went from reasonable for a newbie, to magical. There is
no product that can guarantee that future versions will *always* run older
things. Feel free to argue, but someone can always come up with scenarios
(even if extreme) that wouldn't work.

So, the answer is that you can normally, reasonably expect previously
compiled classes to run in a later JVM. That's much more than most can
promise.

*Generally* deprecated is not a problem, but note that some of these say
"expected to be removed at some point." Now I'll give a real-life example:

Thread.destroy() was never a good idea and actually was never
implemented. At some point, it was changed to throw NoSuchMethodError. No
problem, right? No knowledgeable programmer would ever have used it anyway.

Well, a sometime client of mine, who thinks they can save money by
paying four (and sometimes more) offshore programmers each a third of my
rate, assigned them to a project in which threads were a perfect fit. They
"delivered" a mess which depended on destroy() for cleanup. Now, it didn't
do anything anyway, but under 1.4, it just didn't do anything so the program
ran (if you can call it that.) But try to run it under 1.5 and, you guessed
it: NoSuchMethodError. BTW, the client routinely gets to pay me or others
to clean up after this group while the users suffer non-production quality
applications. But, "it's a corporate direction."

Another example was on another list yesterday. Someone wanted
performance gains in JSF, but couldn't go to JSF 1.2 because one (of an
extremely large number) of their dependencies was Apache Beehive, which
won't play nice with 1.2.

To repeat, the point is you can normally, reasonably expect previously
compiled classes to run in a later JVM, but there are always exceptional
conditions.


Joe Sam

Joe Sam Shirah - http://www.conceptgo.com
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----- Original Message ----- From: "Lim Hock-Chai" <Lim.Hock-Chai@xxxxxxxxxxxxxxx>
To: <java400-l@xxxxxxxxxxxx>
Sent: Friday, March 20, 2009 12:47 PM
Subject: Re: is class file backward compatible

Interesting. Thanks.

"James Perkins" <jrperkinsjr@xxxxxxxxx> wrote in message
news:<mailman.11055.1237566399.26163.java400-l@xxxxxxxxxxxx>...

Deprecated methods for more of a "please don't use me" rather than a

"you

can't use me". They really only show themselves at compile time as

warnings

(or you IDE).

So, you should be fine.
--
James R. Perkins


On Fri, Mar 20, 2009 at 09:13, Lim Hock-Chai
<Lim.Hock-Chai@xxxxxxxxxxxxxxx>wrote:

> So, what will happen if the class, that compiled in the older

version of

> java complier, has a method that is fully deprecated in the new

version

> of JVM?
>
> "David Gibbs" <david@xxxxxxxxxxxx> wrote in message
> news:<mailman.11041.1237564455.26163.java400-l@xxxxxxxxxxxx>...
> > Lim Hock-Chai wrote:
> > > can a class that created using a lower version of java compiler

run

> on a
> > > higher version of JVM?
> >
> > Yes, this should be possible without a problem.
> >
> > david
> >
> >
> >
> > --
> > IBM i on Power - For when you can't afford to be out of business
> --
> This is the Java Programming on and around the iSeries / AS400

(JAVA400-L)

> mailing list
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