Java HotSpot Virtual Machine

Hi,

I have the following situation:
I have a Java GUI ( for testing) with a main.
On the button pressed action method I am creating an ArrayList<Integer> type list with some integers as content.
The java calls a native C code which need to do some work with each element of array. Somewhere is wrong something, but I don't know where, because it seems all OK for me.
With java debugger I have look at ArrayList values and on Java side is ok.

Here is the C code part: -exceptios, error checking, third party missing

// Signature: (Ljava/util/ArrayList;)V
JNIEXPORT void JNICALL Java_mypackage_MyClass_myNativeMethod
(JNIEnv * env, jobject jCalllingObject, jobject alParam)
{
        jclass clsArrayList = env->FindClass("java/util/ArrayList");
	jmethodID midArrayListSize = 0;
	jmethodID midArrayListGet = 0;
	if(clsArrayList != 0){
		midArrayListSize = env->GetMethodID( clsArrayList, "size", "()I");
		midArrayListGet = env->GetMethodID(clsArrayList, "get", "(I)Ljava/lang/Object;");
	}
	jclass clsInteger = env->FindClass("java/lang/Integer");
	jmethodID midIntegerIntValue = 0;
	if(clsInteger != 0){
		midIntegerIntValue = env->GetMethodID(clsInteger, "intValue", "()I");
	}

	if((clsArrayList != 0) && (midArrayListSize != 0)){		
		int arrayListSize = env->CallIntMethod(alParam,  midArrayListSize );//ok

		if((arrayListSize > 0)&& (midArrayListGet != 0) && (clsInteger != 0) && (midIntegerIntValue != 0)){		

			for(int i=0; i<arrayListSize; i++){
				jobject arrayElement = env->CallObjectMethod(alParam,  midArrayListGet);//get: will contain 0 :(
				int intValue = env->CallIntMethod(arrayElement,  midIntegerIntValue);	//intValue						
				//...
			}
			//...		
		}
	}
}

The first error sign I see at

jobject arrayElement = ..

because has the 0 value, like a null pointer.... I have given 2 elements of array eg 400 and 500, so there the 0 isn't good I think.

What is wrong in this code, how can be correct?