JNI help - FindClass

Question

I have recently been trying to play around with JNI, but every time I run my program it says that it cannot locate my file (aka I get the error that it couldn't find the CTF class). I'm currently using xcode on my mac. Here is my code:
* ctf.c
* CTF
#include "JavaVM.framework/Headers/jni.h"
int main() {
JNIEnv *env;
JavaVM *jvm;
JavaVMInitArgs vm_args;
jint res;
jclass cls;
jmethodID cid, mid;
jstring opp_str, opp_str_loc;
jobjectArray args;
jobject class_instance, return_val;
char classpath[4096] = "-Djava.class.path=.:";
/* IMPORTANT: specify vm_args version # if you use JDK1.1.2 and beyond */
vm_args.version = JNI_VERSION_1_4;
JNI_GetDefaultJavaVMInitArgs(&vm_args);
//this is the directory where my CTF.class file is located
char *classpathOption = strcat(classpath, "~/Documents/Research/CTF");
fprintf(stdout, "class path is %s\n", classpathOption);
JavaVMOption options[1];
options[0].optionString = classpathOption;
vm_args.version = 0x00010004;
vm_args.options = options;
vm_args.nOptions = 1;
vm_args.ignoreUnrecognized = JNI_TRUE;
/* Create the Java VM */
res = JNI_CreateJavaVM(&jvm,(void**)&env,&vm_args);
if (res < 0) {
fprintf(stderr, "Can't create Java VM\n");
exit(1);
} else {
printf("created Java VM just fine.\n");
cls = (*env)->FindClass(env, "CTF");
if (cls == 0) {
fprintf(stderr, "Can't find CTF class\n");
exit(1);
cid = (*env)->GetMethodID(env, cls, "<init>", "()V");
if (cid == 0) {
fprintf(stderr, "Can't find CTF constructor\n");
class_instance = (*env)->NewObject(env, cls, cid);
if (class_instance == 0) {
fprintf(stderr, "Can't create CTF class\n");
mid = (*env)->GetMethodID(env, cls, "makePrediction", "([Ljava/lang/String;)V");
if (mid == 0) {
fprintf(stderr, "Can't find CTF.makePrediction\n");
exit(1);
opp_str = (*env)->NewStringUTF(env, "opponent");
if (opp_str == 0) {
fprintf(stderr, "Out of memory\n");
exit(1);
opp_str_loc = (*env)->NewStringUTF(env, "desk");
if (opp_str_loc == 0) {
fprintf(stderr, "Out of memory\n");
exit(1);
args = (*env)->NewObjectArray(env, 2,
(*env)->FindClass(env, "java/lang/String"), opp_str);
if (args == 0) {
fprintf(stderr, "Out of memory\n");
exit(1);
} else {
(*env)->SetObjectArrayElement(env, args, 1, opp_str_loc);
return_val = (*env)->CallObjectMethod(env, class_instance, mid, args);
(*jvm)->DestroyJavaVM(jvm);
return 0;

Answer 1

I'm using java 1.4.2, and jni version 1.4.
Here's the c code:
#include "wwhd.h"
#include "JavaVM.framework/Headers/jni.h"
#include <stdlib.h>
char *wwhd(char** knowledge) {
    JNIEnv *env;
    JavaVM *jvm;
    JavaVMInitArgs vm_args;
     jint res;
    jclass cls;
    jmethodID cid, mid;
    jstring opp_str, opp_str_loc, method_str;
    jobjectArray args;
     jobject class_instance, return_val;
    char classpath[4096] = "-Djava.class.path=.:";
    //JNI_GetDefaultJavaVMInitArgs(&vm_args);
     char *classpathOption = strcat(classpath, getenv("CLASSPATH"));
     classpathOption = strcat(classpathOption, ":");
     classpathOption = strcat(classpathOption, "~/Documents/Research/NRL/Eclipse_Workspace/CTF");
     JavaVMOption options[1];
     options[0].optionString = classpathOption;
     vm_args.version = 0x00010004;
     vm_args.options = options;
     vm_args.nOptions = 1;
     vm_args.ignoreUnrecognized = JNI_FALSE;
         /* Create the Java VM */
        res = JNI_CreateJavaVM(&jvm,(void **)&env,&vm_args);
        if (res < 0) {
            fprintf(stderr, "Can't create Java VM\n");
            exit(1);
        } else {
          printf("created Java VM just fine.\n");
        cls = (*env)->FindClass(env, "CTF_Human");
        if (cls == 0) {
            fprintf(stderr, "Can't find CTF_Human class\n");
           (*jvm)->DestroyJavaVM(jvm);
            exit(1);
        } else {
          fprintf(stdout, "Found CTF_Human class\n");
     cid = (*env)->GetMethodID(env, cls, "<init>", "()V");
     if (cid == 0) {
          fprintf(stderr, "Can't find CTF_Human constructor\n");
          (*jvm)->DestroyJavaVM(jvm);
     } else {
          fprintf(stdout, "Found CTF_Human constructor successfully\n");
     class_instance = (*env)->NewObject(env, cls, cid);
         if (class_instance == 0) {
          fprintf(stderr, "Can't create CTF_Human class\n");
          (*jvm)->DestroyJavaVM(jvm);
     } else {
          fprintf(stdout, "Created CTF_Human class w/out a problem\n");
     cls = (*env)->GetObjectClass(env, cls);
     if (cls == 0) {
         fprintf(stderr, "Can't get CTF_Human class from instance\n");
          (*jvm)->DestroyJavaVM(jvm);
                  exit(1);
          } else {
          fprintf(stdout, "Got CTF_Human class from instance\n");
     mid = (*env)->GetStaticMethodID(env, cls, "main", "([java/lang/String;)V");
         if (mid == 0) {
                  fprintf(stderr, "Can't find CTF_Human.main\n");
          if ((*env)->ExceptionOccurred(env)) {
               fprintf(stderr, "about to exception describe\n");
               (*env)->ExceptionDescribe(env);
               fprintf(stderr, "done exception describing\n");
          (*jvm)->DestroyJavaVM(jvm);
                 exit(1);
    (*jvm)->DestroyJavaVM(jvm);
     return "";          
}and the output is
Running...
created Java VM just fine.
Found CTF_Human class
Found CTF_Human constructor successfully
Created CTF_Human class w/out a problem
Got CTF_Human class from instance
Can't find CTF_Human.main
about to exception describe
java.lang.NoSuchMethodError: main
Exception in thread "main" done exception describing
Debugger stopped.
Program exited with status value:1.(gdb)
The java code (main function) is:
     public static void main(String[] args) {
          String[] arg = new String[2];
          arg[0] = "opponent";
          arg[1] = "desk";
          CTF h =  new CTF();
          System.out.println(h.makePrediction(arg, true, null));  //another fn in the class
          System.exit(0);
     }Thanks for all your help/time...