Java Help - Simple JNI program fails

Author

Simple JNI program fails

Steve Dussinger

2004-05-20, 10:31 pm

Extracting the following C++ code (with some minor mods) from other
posts in this group, I was hoping to at least be able to create a JVM
and grab a class which is pretty much guaranteed to exist. Well, I
can't seem to make the thing work.

Running under the debugger, I can see the JVM get created, but when I
try to find the System class, I get a zero response.

Now near as I can tell, System should always be available, if the JVM
has been initialized at all, but I can't seem to get it to work.

Anyone have any ideas?

Code follows----------------------------

JNIEnv *env;
JavaVM *jvm;
JavaVMInitArgs vm_args;
JavaVMOption options[1];
jint res;
jclass cls;
jmethodID mid;
jstring jstr;
jobjectArray 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 == JNI_ERR) {
printf("Error creating VM\n");
}

cls = env->FindClass("System");
if (cls == 0) {
fprintf(stderr, "Can't find System class\n");
exit(1);
}

-----------------------------------

BTW, it's running on Windows XP, the C++ is written using Visual
Studio.NET 2003 (v 7.1) using the Sun jdk1.4.2_04 VM...

Thanx for any help...

--Steve

Gordon Beaton

2004-05-21, 6:31 am

On 20 May 2004 18:53:18 -0700, Steve Dussinger wrote:
> Extracting the following C++ code (with some minor mods) from other
> posts in this group, I was hoping to at least be able to create a
> JVM and grab a class which is pretty much guaranteed to exist. Well,
> I can't seem to make the thing work.
>
> Running under the debugger, I can see the JVM get created, but when
> I try to find the System class, I get a zero response.

[...]

> cls = env->FindClass("System");

Try this instead:

cls = env->FindClass("java/lang/System");

if (!cls) {
if (env->ExceptionOcurred()) {
env->ExceptionDescribe();
}
}

/gordon

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