Re: status of gcj

[David Daney <ddaney at avtrex dot com>]

Johannes Klarenbeek wrote:
> 2008/9/16 David Daney <ddaney@avtrex.com>:
> > Please keep java@gcc.gnu.org CCed.
> >
> > Johannes Klarenbeek wrote:
> > > 2008/9/15 David Daney <ddaney@avtrex.com>:
> > >
> > > > Johannes Klarenbeek wrote:
> > > >
> > > > > hi there,
> > > > >
> > > > > i looked at the excellent gcj project, but was a little confused about
> > > > > the status of the project. for example...
> > > > >
> > > > > last gcj news flash is at march 30, 2007
> > > > > last cni update is october 22, 2000
> > > > > last classpath update is june 6 of 2008
> > > > The GCJ News is not keep very current.  But there is still work being
> > > > done
> > > > on GCJ and libgcj.
> > > what parts are not very current at the very moment concerning the byte
> > > code implementation of java in gcj?
> > I was talking about the web site.  I'm not sure what your question was
> > though.
>
> oh sorry. i was wondering if the compiler (and interpreter)
> implementation is up to date with the current java sun implementation.
> not referening to the Classpath implementation. for example: does gcj
> implement generics (or what are they called ... templates like
> c++?)... is the java byte code generation by gcj after source code
> compilation equal to the latest java specs etc...


The current (as of 4.3) version no longer generates byte code, nor 
directly compiles .java source files.  Instead we use ecj (Eclipse 
Compiler for Java) to do the java->class compilation.  GCJ then compiles 
the class files (bytecode) into native code.  This give us full java 
generics support.


> > >  i was reading about the gnu compiler collection on wikipedia and
> > > found that the gnu compiler is separeted in two parts (3 really); a
> > > front-end and a back-end. the front-end parses languages like C, C++,
> > > java, ADA, fortran and more. the back-end should support multiple
> > > processor architectures. i guess that gcj is the front-end part in gcc
> > > isn´t it?
> > Correct.
>
> ok, how big is the gcj specific front-end part compared to for example
> c++... did the developers copy a lot of code from the c++ project and
> changed it to fit the java requirements?

GCJ was started many years ago.  I don't know how much was borrowed from 
the C++ compiler, but currently it is completely separate.  As for the 
size, I don't know a good unit to use to measure it.

> since the back-end of gcj produces java byte code as well, does that
> mean one can write c++ programs and compile it to java byte code?
>
> > > > > where is project going too? how is the libgcj doing... is it already
> > > > > obsolete and replaced by classpath?
> > > > For the last several years libgcj has been based on classpath.  So it is
> > > > not
> > > > being replaced by classpath, for the most part it *is* classpath adapted
> > > > to
> > > > work with gcj.
> > > is libgcj a library that implements VMObject, VMString and some calls
> > > for AWT for example? so classpath can call the methods on these native
> > > objects whereas libgcj calls methods on the operating system to draw a
> > > windows for example?? if that is true, does libgcj support besides
> > > xlib also win32?
> > That is the basic idea, but the specifics are slightly different.  For the
> > case of Object, String, Class, and several other classes in the java.lang
> > package, libgcj completely replaces the classpath implementation.  For some
> > of the I/O classes libgcj does implement the VM* interfaces.  The majority
> > of the code in classpath does not have VM dependencies, so the gcj specific
> > parts of libgcj are a small percentage of the total code.
>
> sorry, i lost you there... the gcj specific parts of libgcj are a
> small percentage of the total code? what do you mean? leaving
> Classpath out of the story, the code generated from source by gcj
> links to libgcj isn´t it?

The entire java runtime library is quite large.  For gcj the runtime 
library is called libgcj.  The amount of gcj specific code in libgcj 
that differs from the classpath project is small compared to the total 
amount of classpath code used.

All code compiled by gcj must be linked to libgcj to be useful.

> another question, maybe a little off topic since its a classpath
> related question. just out of curiousity, can a bsd licensed java
> compiler use the classpath library?


Read the classpath license.

David Daney