Re: Invoking JNI function using gcj

[Andrew Haley <aph at redhat dot com>]

Vaijayanthi Mala Suresh wrote:
> I have written an HelloWorld.java as given below
> 
> public class HelloWorld {
>    public native void natPrint();
> 
>    public HelloWorld()
>    {
>      System.out.println("Hello from constructor");
>    }
>    public void printline()
>    {
>      System.out.println("Hello from printline");
>  natPrint()
>    }
>    public static void main(String [] args) {
>      System.out.println("Hello from main");
>      HelloWorld ht = new HelloWorld();
>      ht.printline();
>    }
> static
> {
>  System.loadLibrary("HelloWorld");
> }
>  }
> 
> I have compiled it with gcj as given below
> gcj -c -fjni HelloWorld.java
> gcj -C HelloWorld.java
> gcjh HelloWorld
> gcjh -jni HelloWorld -o HelloNative.h
> gcjh -stubs -jni HelloWorld
> g++ -I. -c HelloWorld.c natHelloWorld.o
> gcj -shared natHelloWorld.o -o libHelloWorld.so

You can't mix JNI and CNI like this.  Don't use the -jni commands.

> Copied the .so file into the folder as /lib and it set in LD_LIBRARY_PATH.
> 
> I have a cppstartup.cpp which does the JVM Initialization and has
> invokes HelloWorld as given below
> 
> #include "HelloWorld.h"
> 
> using namespace java::lang;
> 
>       try
>       {
> JvCreateJavaVM(NULL);
> JvAttachCurrentThread(NULL, NULL);
> 
>       String *message = JvNewStringLatin1("Hello from C++");
>       JvInitClass(&System::class$);
>       System::out->println(message);
> 
>   HelloWorld *ht = new HelloWorld();
>       ht->printline();
> 
>       JvDetachCurrentThread();
>       }
>       catch (Throwable *t)
>       {
>         System::err->println(JvNewStringLatin1("Unhandled Java exception:"));
>        t->printStackTrace();
>       }
> 
> This throws an exception  me "Unsatisfied Linker Error"
> 
> Can someone help me in this regard?

It doesn't even compile for me.  Your cppstartup.cpp is incomplete.

Andrew.