Java Native Interface Exception Access Violation

Question

Ok i have two programs One that works and one that dosn't
the one that works is a javaMethod that calls a C method. the C method then uses a callsback on a java method that returns an array of integers. that works fine
the Second program uses the same c side code and the same Java Methods from the original are implemented into a program i have that runs a Jframe. anyways when i run this program the Native side does all of its tasks but when its done it crashes Evrything
here is the Native Code
#include <jni.h>
#include "MyNativeInterface.h"
#include <stdio.h>
JNIEXPORT void JNICALL
Java_MyNativeInterface_sayHello(JNIEnv *env, jobject obj)
printf("Hello world!\n");
return;
JNIEXPORT void JNICALL
Java_MyNativeInterface_nativeMethod(JNIEnv *env, jobject obj)
jintArray arr;
     jint len;
     int *carr;
     int i;
jclass cls = (*env)->GetObjectClass(env, obj);
jmethodID mid =
(*env)->GetMethodID(env, cls, "callback", "()[I");
if (mid == NULL) {
return; /* method not found */
printf("In C\n");
arr = (*env)->CallObjectMethod(env, obj, mid);
     len = (*env)->GetArrayLength(env,arr);
     printf("Array Length = %d\n",len);
     carr = (int*)malloc(len);
     (*env)->GetIntArrayRegion(env,arr,0,len,(jint*)carr);
     for (i=0;i<len;i++)
printf("Array position %d is %d \n",i,carr);
and here is the java class that deals with the native side
import java.util.*;
public class MyNativeInterface extends Object {
private TextAreaDemo gui ;
public MyNativeInterface (TextAreaDemo guiRecieved)
gui = guiRecieved;
static {
System.loadLibrary("hello");
public boolean sendLocoMessage ( byte [] bytesToSend )
try {
System.out.println("number Of Tokens ="+bytesToSend [0]);
} catch (Exception e) {
System.out.println("didn't even get inside2 ok ");
return true;
public void receiveLocoMessage ( byte [] bytesToSend ){
gui.AddMessage ("WOOOOO HOOOOOO");
public native static void sayHello ();
public native void nativeMethod();
private int [] callback() {
int cools [] = new int [32] ;
int i = 0 ;
for (i=0;i<32;i++)
cools [i] = i;
//System.out.println("In Java");
return cools;
the Say Hello Method works just fine
and the array for the C side prints out just fine
then evrything crashes with the following message
An unexpected exception has been detected in native code outside the VM.
Unexpected Signal : EXCEPTION_ACCESS_VIOLATION occurred at PC=0x6D3276E4
Function=ZIP_Open+0x107
Library=c:\j2sdk1.4.0_01\jre\bin\zip.dll
and a whole BUNCH of current java thread stuff and a list of dynamic libraries.
anyways thanks

Answer 1

Your C code asks for the length of the array, then
allocates that many BYTES using malloc. This looks
bogus to me.I agree.
Maybe something like this would be better:
carr = (int*)malloc(len * sizeof jint);