linker - GCJ Linking Error: Says error: undefined reference to 'main' collect2: error: ld returned 1 exit status -

linker - GCJ Linking Error: Says error: undefined reference to 'main' collect2: error: ld returned 1 exit status -

the code this:

public class thingy { public static void main(string[] args) { system.out.println(math.random()); } }

so, absolutely not unusual case, basic example.

when seek utilize gcj's javac implementation create bytecode instead of openjdk one, works fine.

neil@neil-inspiron-m5030:~/javastuff$ javac thingy.java neil@neil-inspiron-m5030:~/javastuff$ java thingy 0.2794511843566371

but when seek gcj create native code, linker error. if want, can give verbose output:

neil@neil-inspiron-m5030:~/javastuff$ gcj --verbose thingy.java using built-in specs. reading specs /usr/lib/gcc/x86_64-linux-gnu/4.7/libgcj.spec rename spec startfile startfileorig rename spec lib liborig collect_gcc=gcj collect_lto_wrapper=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper target: x86_64-linux-gnu configured with: ../src/configure -v --with-pkgversion='ubuntu/linaro 4.7.2-1ubuntu1' --with-bugurl=file:///usr/share/doc/gcj-4.7/readme.bugs --enable-languages=c,c++,java --prefix=/usr --program-suffix=-4.7 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-libmudflap --enable-plugin --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.7/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.7 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.7 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu thread model: posix gcc version 4.7.2 (ubuntu/linaro 4.7.2-1ubuntu1) collect_gcc_options='-fsaw-java-file' '-v' '-fbootclasspath=./:/usr/share/java/libgcj-4.7.jar' '-g1' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/4.7/ecj1 thingy.java -g1 -fbootclasspath=./:/usr/share/java/libgcj-4.7.jar -g1 -fsource=1.5 -ftarget=1.5 -fzip-dependency /tmp/cckwg5ag.zip -fzip-target /tmp/ccbixa8g.jar collect_gcc_options='-fsaw-java-file' '-v' '-fbootclasspath=./:/usr/share/java/libgcj-4.7.jar' '-g1' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/4.7/jc1 /tmp/ccbixa8g.jar -fsource-filename=thingy.java -fhash-synchronization -fno-use-divide-subroutine -fuse-boehm-gc -fnon-call-exceptions -fkeep-inline-functions -quiet -dumpbase thingy.java -mtune=generic -march=x86-64 -auxbase thingy -g1 -version -fsaw-java-file -fbootclasspath=./:/usr/share/java/libgcj-4.7.jar -faux-classpath /tmp/cckwg5ag.zip -o /tmp/cclzeoej.s gnu java (ubuntu/linaro 4.7.2-1ubuntu1) version 4.7.2 (x86_64-linux-gnu) compiled gnu c version 4.7.2, gmp version 5.0.2, mpfr version 3.1.0-p3, mpc version 0.9 ggc heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 gnu java (ubuntu/linaro 4.7.2-1ubuntu1) version 4.7.2 (x86_64-linux-gnu) compiled gnu c version 4.7.2, gmp version 5.0.2, mpfr version 3.1.0-p3, mpc version 0.9 ggc heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 class path starts here: /tmp/cckwg5ag.zip/ (zip) ./ (system) /usr/share/java/libgcj-4.7.jar/ (system) (zip) collect_gcc_options='-fsaw-java-file' '-v' '-fbootclasspath=./:/usr/share/java/libgcj-4.7.jar' '-g1' '-shared-libgcc' '-mtune=generic' '-march=x86-64' -v --64 -o /tmp/ccziy0ol.o /tmp/cclzeoej.s gnu assembler version 2.22.90 (x86_64-linux-gnu) using bfd version (gnu binutils ubuntu) 2.22.90.20120924 compiler_path=/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/ library_path=/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../:/lib/:/usr/lib/ collect_gcc_options='-fsaw-java-file' '-v' '-fbootclasspath=./:/usr/share/java/libgcj-4.7.jar' '-g1' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/4.7/collect2 --sysroot=/ --build-id --no-add-needed --as-needed --eh-frame-hdr -m elf_x86_64 --hash-style=gnu -dynamic-linker /lib64/ld-linux-x86-64.so.2 /usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o /usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crti.o /usr/lib/gcc/x86_64-linux-gnu/4.7/crtbegin.o -l/usr/lib/gcc/x86_64-linux-gnu/4.7 -l/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu -l/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../lib -l/lib/x86_64-linux-gnu -l/lib/../lib -l/usr/lib/x86_64-linux-gnu -l/usr/lib/../lib -l/usr/lib/gcc/x86_64-linux-gnu/4.7/../../.. /tmp/ccziy0ol.o -lgcc_s -lgcc -lgcj -lm -lpthread -lrt -lz -ldl -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-linux-gnu/4.7/crtend.o /usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crtn.o /usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o(.text+0x20): error: undefined reference 'main' collect2: error: ld returned 1 exit status

so, suppose question is, have thought might have went wrong?

i guess need add together --main=thingy command. since several classes may have 'main' method, linker needs told 1 use.

also, might want add together -o <name of executable>, otherwise, you'll 'a.out' file, default executable name gnu compilers (and c compiler actually).

regards

linker ld binutils gcj