JAVAROOT was already defined

[Simon Josefsson]

The Makefile.am below generate the following errors during autoreconf:

...
configure.ac: installing `./install-sh'
configure.ac: installing `./missing'
Makefile.am: installing `./INSTALL'
doc/Makefile.am:28: installing `doc/mdate-sh'
doc/Makefile.am:28: installing `doc/texinfo.tex'
examples/Makefile.am: installing `./depcomp'
/usr/share/automake-1.8/am/java.am: JAVAROOT was already defined in condition 
ENABLE_JAVA, which is included in condition TRUE ...
java/Makefile.am:35:   while processing `libidn_jar_JAVA'
java/Makefile.am:29: ... `JAVAROOT' previously defined here
/usr/share/automake-1.8/am/java.am: JAVAROOT was already defined in condition 
ENABLE_JAVA, which is included in condition TRUE ...
java/Makefile.am:35:   while processing `libidn_jar_JAVA'
java/Makefile.am:29: ... `JAVAROOT' previously defined here
autoreconf: Leaving directory `.'
$ 

I don't understand the warning.  JAVAROOT appears to be documented as
a user variable.  Am I not allowed to modify it?  From the manual:

`JAVAROOT'
     The value of this variable is passed to the `-d' option to
     `javac'.  It defaults to `$(top_builddir)'.

Thanks,
Simon

PS. There are more problems with the snippet, I received it as a
contribution and I'm just starting to integrate it.  Don't worry about
those.

SUBDIRS = gnu

# Only execute this if configure was running with --enable-java
if ENABLE_JAVA

EXTRA_DIST = README.html

CLEANFILES = $(libidn_jar_DATA)

JAVAROOT = .

# Install libidn.jar into the prefix/lib directory
libidn_jardir = $(libdir)

# All files are in the gnu.inet.encoding package
libidn_jar_JAVA = gnu/inet/encoding/*.java

# So are the resulting class files
libidn_jar_CLASSES = gnu/inet/encoding/*.class

libidn_jar_DATA = libidn.jar

# .jar files are not yet created automatically by automake, are they?
libidn.jar:
        $(JAR) cf libidn.jar $(libidn_jar_CLASSES)

endif # ENABLE_JAVA