Re: Compiling java (gcj, jikes, kaffe...)

[D-Man <dsh8290@rit.edu>]

On Sat, Jan 27, 2001 at 08:43:04PM +0100, Andreas Hetzmannseder wrote:
| Dear debian-users,
| 
| This is really stupid, but I don't know any further.
| Every time I try to compile some java source code - actually the HelloWorld
| example from the Debian Java FAQ - I get error messages: 
| 
| with gcj:
|     /usr/lib/crt1.o: In function `_start':
|     /usr/lib/crt1.o(.text+0x18): undefined reference to `main'
|     collect2: ld returned 1 exit status

gcj outputs C++ object files from the Java source.  Then (unless you
gave it the -c option) it links it to form an ELF binary (just like
C/C++).  The problem is the linker can't find main.

int main( int argc , char** argv )
{
	/* ... */
	return 0 ;
}


The solution is to tell gjc where main is:

gcj --main=MyJavaClassDefiningMain *.java


gcj will then run a script (installed with it) to spit out some C/C++
code with the appropriate main() function that will call the main you
defined in your Java class.  If you give gcj the -c option it will
stop when it has produced C++ object files (.o).  You can then link
them at the end.

gcj also has a -C option will tells it to output Java bytecodes
(.class) instead.  These will then need some JVM (jre, kaffe, etc) to
run.

| 
| with jikes:
|     Found 2 system errors:
| 
|     *** Error: Could not find package named
|         /usr/share/java/repository/java/util
| 
|     *** Error: Could not find package named
|         /usr/share/java/repository/java/lang
| 

The packages java.util and java.lang can't be found by the compiler.
I haven't used jikes before so I can't be more specific.  Maybe a
CLASSPATH problem?

| with kaffe's kjc:
|     java.lang.NoClassDefFoundError: at/dms/kjc/Main
|         at java.lang.Throwable.<init>(Throwable.java:38)
|         at java.lang.Error.<init>(Error.java:21)
|         at java.lang.LinkageError.<init>(LinkageError.java:21)
|         at java.lang.NoClassDefFoundError.<init>(NoClassDefFoundError.java:21)
| 

I guess that kjc is a shell script that tries to run a java program.
Apparently the main() function here is in the class "Main" in the
package "at.dms.kjc" and the class can't be found.  This is definitely
a CLASSPATH problem.  

When I tried out kaffe, it had the commands "javac" for compiling and
"java" for executing bytecodes.  I think they were really just
symlinks to the kaffe commands.  Perhaps trying these commands will
help?

| BTW: Running ready programs with kaffe works just fine...
| 
| I put the following entry into my ~/.profile:
| export CLASSPATH=/usr/share/kaffe

I would recommend against this.  At my present job I am using a Win2k
box (with cygwin of course) and Sun's jdk.  I found it is much better
to make a whole collection of shell scripts that execute the proper
JVM (I have 1.1.8, 1.2.2, and 1.3 installed) with the proper classpath
stuff on the command line.  For Sun's jdk, the "-classpath <system
specific path list>" option set the classpath.  For jdk1.1.8
classes.zip must be listed in the option, for jdk1.2+ rt.jar is found
automagically (but tools.jar must be included to use ant -- a make
replacement for java devel).

The funny thing is the classpath must be in DOS/Windows format (with
d:, etc and semicolons as the separator) but I use cygwin's bash for
my shell.  I always have to put the path list in quotes and escape all
the backslashes.  It's quite a pain.  Why did MS have to use the
escape character for the directory separator?  POSIX paths are much
easier to deal with IMO.

| 
| Could someone please tell me what is wrong or missing? 
| Thanks in advance,
| Andreas.
| 

HTH,
-D