Re: getting started with classpath

[John Leuner]

> I have a gnawing interest in hacking on classpath, and I have read 
> a couple of times over the guide "hacking.html" that is linked from 
> the GNU site.  It's just, I'm having a simultaneous-learning-curve 
> experience, and I'm wondering if anyone on this list can push me 
> off in the right direction to eventually being able to contribute.
> 
> 
> My "problems" or rather questions are as follows:
> 1.  I only have experience using one JDK/JRE (Sun's), although I 
> have used it on many platforms.  I noticed a strong linkage between 
> Classpath and (of course) the free JVM / compiler implementations.
> That's cool, I get it, I am just not sure which components each 
> of these tools replace, and what their level of compliance / implementation 
> is.  Is there maybe a best order to learn about these tools in?  
> I would like to know Free Java and work on it even, but am not sure 
> how to start.

Well, I suggest you start with compilers. Try out jikes (it's quite similar to 
javac in behaviour) and move on from there to kjc.

Next try and compile classpath itself.

After that, get one of the free JVMs and try to get it to work with Classpath. 

You can also try out gcj.

If you encounter anything 'surprising' with these tools, it's worthwhile to 
post the list, because ultimately we would want to provide a similar 
user-experience to that provided by the SUn software.

> 2.  How can I be certain I meet the "clean room" requirement?  I 
> have browsed through several of sun's classes several times in source 
> code form as included on my Mac OS X machine.  I know that I don't 
> remember any specifics, they were just instructive at the time.  
> Does this count?

Yes
 
> 3. If I write "pure java" implementations, do I need to worry much 
> about your notes on native code and VM integration?  I have not done 
> any JNI programming, but I am okay with learning.  I guess, a better 
> question is, what is the view of this project as far as native code,
> VM integration, etc.?  I get the feeling by browsing the classes 
> that there isn't much native code in the non-GUI components.

Generally we try to minimize use of native code. IMO there are still some 
classes that could do with pure Java where native code is being used. You don't 
really need to worry much about native code and VM integration unless you're 
hacking the 'core' classes. In fact these classes have received the most 
attention and are probably in the best state. What needs more work is stuff 
that isn't used so often.
 
> Any "getting started" tips would be much appreciated -- it seems 
> like there's a lot to learn for someone coming from a pure Sun world 
> as far as the raw implementation goes.

Well, in the Sun world you don't have to worry much about the implementation 
because it's closed :-)

(Ok, maybe the source to the class libraries is available for viewing, but it's 
not available for potential modification).

You might struggle a bit with the various VMs since they are at various stages 
of maturity and not always in sync with the ever-changing Classpath. Don't 
hesitate to ask the VM developers or Classpath developers questions about 
getting things to work.

John Leuner