Run Time Error in 'return functions->FindClass(this, name)'

[ravi120486]

Hi all, Iam getting run time error in following function in jni.h: return functions->FindClass(this, name); Following is the FindClass() function call fron my cpp file: cls = (env)->FindClass(servParams[i].lib); Plz help , I am new to JNI Programming. :(

[Lost User]

What is the actual error code or message that you receive? Also check the values of the various parameters you send to your functions. I also do not see the connection between the above two statements, the first accepts two parameters and the second passes only one.

It's time for a new signature.

[ravi120486]

Actually in jni.h following is the definition of FindClass

jclass FindClass(const char *name) {
return functions->FindClass(this, name); }

Following is the Error message I am getting at 'FindClass(this, name)': Unhandled exception at 0x60edf3a0 (xxx.dll) in yyy.exe: 0xC0000005: Access violation reading location 0x00000000.

[Lost User]

OK so trying to read memory address 0 indicates you have an uninitialized pointer. Check your code to see where your pointers are set up. More specifically check the code where you are calling FindClass() and ensure that your name parameter actually points to something.

It's time for a new signature.

[ravi120486]

Hey Richard, Here in 'FindClass(this, name)' name parameter is pointing to some value but 'this' pointer is pointing to 0x00000000. Plzz help........

[Lost User]

ravi120486 wrote:

Plzz help.

You will need to show some of your code, both Java and C for me to have any possibility of seeing how you are getting to this point. BTW please don't rely to your own messages as I don't get a notification of the update.

It's time for a new signature.

[ravi120486]

I am not posting the entire code,Tell me if its sufficient Following is my Code:

int MyAPI(Parameters* Params, int i) {
.
.
.
JNIEnv *env;
JavaVM *jvm;
JavaVMInitArgs vm_args;
char clspath[400]="-Djava.class.path=";

resCheckVM = JNI\_GetCreatedJavaVMs(&jvm, bufLen, &nVMs);
if( resCheckVM < 0 || nVMs < 1 )
{
.
.
.
 JNI\_GetDefaultJavaVMInitArgs(&vm\_args);
 fflush(stdout);
 res = JNI\_CreateJavaVM(&jvm,(void\*\*)&env,&vm\_args);
 if (res < 0)
     fprintf(stderr, "Failed to Create JVM.\\n");
 }
else
{
 fflush(stdout);
 res = (jvm)->AttachCurrentThread((void\*\*)&env, NULL);
 if (res < 0)
   fprintf(stderr, "Failed attaching current thread to JVM.\\n");
 }
	 
cls = (env)->FindClass(Params\[i\].lib);

if (cls == 0)
{
  fprintf(stderr, "Can't find Prog class \\n",Params\[i\].lib);
  return 1;
}
    {
      fprintf(stderr, "Can't find function \\n");
      return 1;
     }

.
.
.

	 return 0;

}

Here I am getting this message "Failed to Create JVM." Then a run time error at FindClass(Params[i].lib).

[Lost User]

ravi120486 wrote:

Here I am getting this message "Failed to Create JVM."

Well, I don't think anything will work after this. If you have not managed to instantiate the JVM then your application should die as there is nothing further it can do.

It's time for a new signature.

[ravi120486]

Hey Richard, Can u tell me the reasons why JVM creation might have failed , so that i can loook for it . Regards, Ravi

[Lost User]

You should check the JNI error code returned from your call to JNI_CreateJavaVM(); I would also check the values of your input parameters prior to the call to ensure all are correct.

It's time for a new signature.

[Lost User]

Ravi, I have been doing some more testing and figure that some of your code is not needed and some needs correcting.

• The call to JNI_GetCreatedJavaVMs() will never succeed as you do not have any created VMs at that point. Also this call is not used in newer versions so can be removed.
• The call to JNI_GetDefaultJavaVMInitArgs() is no longer necessary and does not serve any purpose.
• Before calling JNI_CreateJavaVM() you need to initialize your vm_args structure with the correct values as described here[^]

It's time for a new signature.