g++ 4.1 compiling against libgcj; classes cannot inherit from Object?

Thu Dec 8 20:31:00 GMT 2005

I'm trying to make a simple hello world program wherein I have a C++
object that inherits from java::lang::Object. When I try to compile
the program with g++, it gives me the following error:
$ make
/opt/gcc-4.1/bin/g++ -o hello hello.java.cpp -L/opt/gcc-4.1/lib -lgcj
/tmp/ccSrbVBE.o: In function `hidden alias for Hello::Hello()':
hello.java.cpp:(.gnu.linkonce.t._ZN5HelloC1Ev+0xd): undefined
reference to `java::lang::Object::Object()'
hello.java.cpp:(.gnu.linkonce.t._ZN5HelloC1Ev+0x12): undefined
reference to `vtable for Hello'
collect2: ld returned 1 exit status
make: *** [hello] Error 1
So, it looks like it can't find Object::Object(), but when I do nm -C
/opt/gcc-4.1/lib/libgcj.so, I get
...
006b1e40 T java::lang::Object::Object()
...
So, it looks like the Object contructor is there. Does anyone know
what I have to do to inherit from Object with a c++ class? The docs
imply that it's possible, but I can't make it work. The complete
source follows:
hello.java.cpp:
#include <gcj/cni.h>
#include <java/lang/Object.h>
#include <java/lang/System.h>
#include <java/lang/String.h>
#include <java/io/PrintStream.h>
#include <java/lang/Throwable.h>
class Hello : public java::lang::Object {
 public:
 static java::lang::Class class$;
 Hello() {
 JvInitClass(&class$);
 }
 java::lang::String* sayHello() {
 using namespace java::lang;
 String *message = JvNewStringLatin1("Hello from C++");
 JvInitClass(&System::class$);
 System::out->println(message);
 return message;
 }
};
java::lang::Class Hello::class$;
int main() {
 try
 {
 JvCreateJavaVM(0);
 JvAttachCurrentThread(0, 0);
 Hello* hello = new Hello;
 hello->sayHello();
 JvDetachCurrentThread();
 }
 catch (java::lang::Throwable *t)
 {
 java::lang::System::err->println(
 JvNewStringLatin1("Unhandled Java exception:"));
 t->printStackTrace();
 }
}