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Re: JNI accessing a class that instantiates another class

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On Aug 15, 1:06 pm, Florian Weimer <f...@deneb.enyo.de> wrote:
> * Danno:
>
> > I'm taking my first stab at JNI.  I have a main Java class that
> > instantiates another class.  In my C++ code, I am using the FindClass
> > function for the main class and calling the method in the main class
> > using GetStaticMethodId/CallStaticIntMethod.  The C++ code is
> > successfully finding the Java class and calling the method that I
> > specified in the GetStaticMethoId function.  The only problem is, when
> > the Java class attempts to create an instance of this second, inner
> > class, it dies.  I don't get an error, it just doesn't work.
>
> Please post code demonstrating the problem.  Have you checked if
> -Xcheck:jni reports anything useful?

Thank you for taking the time to reply to my post.  I have attached my
code below.  I have not used -Xcheck:jni before.  I may not fully
understand how to use it, but the way I understand it, it is a command
line argument.  The java program, however, is not being called from a
command line.  I have a MicroFocus COBOL program that is calling a C++
dll that starts a JVM and invokes a Java method via JNI.  Is there a
way to run -Xcheck:jni under that scenario?

Here is my code...

C++:
#include <jni.h>
#include <windows.h>
#include <string>
#include <stdio.h>
#include <stdlib.h>
#include "IGVIEWER_JNI.H"

using namespace std;

bool initJNI() {
        JNILoaded = false;
        JavaVMOption options[1];
        JavaVMInitArgs vm_args;
        long status;

        options[0].optionString = "-Djava.class.path=.";
        memset(&vm_args, 0, sizeof(vm_args));
        vm_args.version = JNI_VERSION_1_4;
        vm_args.nOptions = 1;
        vm_args.options = options;
        status = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);

        if (status == 0) {
                cls = env->FindClass("IgViewerJNI");
                if(cls ==0) {
                        jvm->DestroyJavaVM();
                        return false;
                } else {
                        JNILoaded = true;
                        return true;
                }
        }
        else {
                return false;
        }

}

extern ULONG WINAPI IMGINIT_JNI () {
        jmethodID mid;
        bool bResults;

        if (!JNILoaded) {
                bResults = initJNI();
                if (!bResults) {
                        return 8;
                }
        }

        mid = env->GetStaticMethodID(cls, "initializeViewer", "()I");
        if(mid !=0) {
                return env->CallStaticIntMethod(cls, mid);
        } else {
                return 8;
        }


}




Java:

import javax.swing.JOptionPane;


public class IgViewerJNI {

        public static int initializeViewer(){

                try {
                        // ** THIS IS WHERE IT DIES - I didn't include
the IgViewerInit class code since it seemed unnecessary.
                        IgViewerInit viewInit = new IgViewerInit();
                        return viewInit.initializeViewer();
                } catch (Exception e) {
                        JOptionPane.showMessageDialog(null, "Error - "
+ e.getMessage());
                        return 8;
                }
        }

        public static void main(String args[]) {


        }

}

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Thread

JNI accessing a class that instantiates another class Danno <danmwall-google@yahoo.com> - 2011-08-15 07:55 -0700
  Re: JNI accessing a class that instantiates another class Florian Weimer <fw@deneb.enyo.de> - 2011-08-15 19:06 +0200
    Re: JNI accessing a class that instantiates another class Danno <danmwall-google@yahoo.com> - 2011-08-15 12:28 -0700
      Re: JNI accessing a class that instantiates another class Florian Weimer <fw@deneb.enyo.de> - 2011-08-15 21:50 +0200
  Re: JNI accessing a class that instantiates another class Roedy Green <see_website@mindprod.com.invalid> - 2011-08-15 15:10 -0700

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