C program: Runtime error from GetStaticMethodId()

Question

I am new to Java and need help with .....
I want to call a java method (native) from legacy C code.
The java code has to return a Hashtable to the C code.
My java works and I wrote another java file to call it. That
also works fine and I can display my new Hashtable in
the calling java code.
However in my calling C code I get a runtime error when
executing mid2 = GetStaticMethodId() // mid2 returns 0
I believe the problem is in the method signature. If I
make it an int method, it runs and returns an int
but I want a hashtable to be returned.
Using javah RMHash, produces RMHashData.h with nothing useful in it.
My environment is: NT, jdk1.3, VIsual Studio cl.
I hope someone can help me.
Sample java code: This runs OK stand alone or called
from another piece of java code.
import java.util.Hashtable;
import java.io.*;
import java.util.*;
public class RMHashData
public RMHashData()
public static Object getMasterData()
Hashtable hash = new Hashtable(20);
int rtnInt = 6;
hash.put ("1050", new String("AAAAAA"));
hash.put ("1051", new String("BBBBB"));
hash.put ("1052", new String("CCCCCCCCC"));
return hash;
public static void main(String[] args)
int RtnInt;
Hashtable RtnHash;
RtnHash = (Hashtable)RMHashData.getMasterData();
Sample C code: (I had to retype this so cut out superfluous code)
#include <stdio.h>
#include <jni.h>
main()
JNIEnv *env;
JavaVM *jvm;
JavaVMOption options[4];
JavaVMInitArgs vm_args;
jint res;
jclass cls;
jmethodID mid, mid2;
jstring jstr;
jvalue result;
jobjectArray args;
char classPath[256];
char libraryPath[256];
vm_args.version = JNI_VERSION_1_2;
/* set the options to pass to the VM */
sprintf(classPath, "%s", "-Djava.class.path=c:\\data\\java_dev\\src");
sprintf(libraryPath, "%s", "-Djava.library.path=c:\\jdk131\\lib");
options[0].optionString = classPath;
options[1].optionString = libraryPath;
vm_args.options = options;
vm_args.nOptions = 2;
vm_args.ignoreUnrecognized = JNI_FALSE;
/* Create the Java VM */
res = JNI_CreateJavaVM(&jvm, (void **) &env, &vm_args);
cls = (*env)->FindClass(env, "RMHashData");
// *** Getting the main method works
mid = (*env)->GetStaticMethodID(env, cls, "main", "([Ljava/lang/String;)V");
// *** Getting this method FAILS
mid2 = (*env)->GetStaticMethodID(env, cls, "getMasterData", "()[Ljava/lang/Object;");
if (mid2 == 0) // ***** mid2 is 0
fprintf(stderr, "Can't find Prog.getMasterData\n");
return 1;
result.l = (*env)->CallStaticObjectMethod (env,cls, mid, args);
// Then comes more fun to pull apart the hashtable...

Answer 1

Bill, Thank you very much - that was it!!!!!
Not sure about your comment...
Comment: Why don't you just return a Hashtable?The line: return hash;
in getMasterData() does exactly that.
If you mean my declaration of the method:
public static Object getMasterData()
where Object should be Hashtable.
I thought the type in the declaration had to match the
JNI call - CallStaticObjectMethod(). I notice there is no
CallStaticHashtableMethod(). Well that is my guess and I only started looking at Java a few days ago and have lots to learn. Thank you again.
Ron...