Java HotSpot Virtual Machine

I got a problem with "CallIntMethod". I try to use a java method to pass a number to a C++ method,and print it in that C++ method. But i let java pass something like 1,2,3.. the C++ method only print '0'.

/* my java code: */

public class returnInt{
		public int reInt(){
		int i = 3;
		return i;
	}
}

/* my C++ code*/
.......
/* Get the "returnInt" class. */
java_class = env->FindClass("returnInt");
if (java_class == NULL) {
cout << "error finding 'Foo' class\n" << endl;
}

/* Get the "enterInt" method ID. */

   method_id = env -> GetMethodID(
     java_class,
     "reInt",
     "()I"
   );
   if (method_id == NULL) {
     cout << "error finding 'reInt' method\n" << endl;
   }
   
    
   /* Call returnInt::reInt . */
   int javaint;
   javaint = env -> CallIntMethod(
     java_class,
     method_id,
     NULL /* args */
   );   
   
   /* print javaint */
   cout << javaint << endl;
...............

I think there must be some mistakes in my code..
How to use the "CallIntMethod"?