Thread: JNI CallStaticVoidMethod crash when Java variables declared outside method

I have started learning JNI to call C/Objective C from Java.
I have a simple java class like this where int i is declared and assigned within the setValue method:

// --------JAVA CLASS EXAMPLE 1

public class Test {

private native void _start();

private void setValue(string str) {
int i;
i = 6;
System.out.println(str);
}
}

The corresponding C/Objective C code does a callback to Java using CallStaticVoidMethod.

// ----------------JNI function in Objective C

JNIEXPORT void JNICALL Java_org_test_try__start
(JNIEnv * env, jobject obj){


JNF_COCOA_ENTER(env);

jobject myObject = (*env)->NewGlobalRef(env, obj);
jclass myClass = (*env)->GetObjectClass(env, myObject);
jmethodID myMethod = (*env)->GetMethodID(env, myClass, "setValue", "(Ljava/lang/StringV");
char* str = "Confirmed";
jstring js = (*env)->NewStringUTF( env, str );
(*env)->CallStaticVoidMethod(env, myClass, myMethod, js);

JNF_COCOA_EXIT(env);
}

This all works fine.
However, if I declare the int i in the java class and not inside the method as follows, the JVM crashes.

// --------JAVA CLASS EXAMPLE 2

public class Test {

private int i;

private native void _start();

private void setValue(string str) {;
i = 6;
System.out.println(str);
}
}

It SEEMS the callback can't access the int variable when it is declared at class level.
Why is this and how can I fix that?

Hi SGARCH,

By the looks of things you are invoking CallStaticVoidMethod on a Non-Static method. This should be erroneous.

Change this to be CallVoidMethod, and you might have more luck. Looks like the JVM might be trying to invoke it as a static, in which case the reference to i in the second example wouldn't work, as i is not static.

Many thanks for your help - so simple now that I see it. CallVoidMethod works fine.