Convert jobject to Integer in JNI C++ and parse the intValue - java-native-interface

Question

I have following code which accepts int value at JAVA level
dataObj.property(20);
This is the definition of property function
void property(Object value){
// JNI called
}
JNI function definition
Java_com_XXX_XXXX_JNIProperty(JNIEnv *a_pEnv, jclass, **jobject a_oPropertyValue**) {
// how to convert jobject to Integer object and then get the intValue
jclass cls = a_pEnv->FindClass("java/lang/Integer");
jmethodID getVal = a_pEnv->GetMethodID(cls, "intValue", "()I");
int i = a_pEnv->CallIntMethod(value, getVal);
}
How to convert jobject which was of type Object in Java to Integer object in JNI and parse int value ?

Answer 1

For a class in Java
public class PassObject {
public static native void displayInt(Object obj);
public static void property(int value) {
PassObject.displayInt(value);
}
public static void main(String[] args) {
PassObject.property(44);
// make sure to be careful in your case,
// as you make assumption that "Object" will be of type "Int"
// It's really easy to be very nasty.
PassObject.displayInt("44");
}
}
you can use following JNI code
JNIEXPORT void JNICALL Java_recipeNo055_PassObject_displayInt
(JNIEnv * env, jclass obj, jobject objarg) {
jclass cls = (*env)->GetObjectClass (env, objarg);
jmethodID integerToInt = (*env)->GetMethodID(env, cls, "intValue", "()I");
jint result = (*env)->CallIntMethod(env, objarg, integerToInt);
printf("Passed value: %d\n", result);
}
if you want to be extra careful, you can always do
jclass cls = (*env)->GetObjectClass (env, objarg);
if( (*env)->IsInstanceOf(env, objarg, (*env)->FindClass(env, "java/lang/Integer")) ) {
jmethodID intValue = (*env)->GetMethodID(env, cls, "intValue", "()I");
jint result = (*env)->CallIntMethod(env, objarg, intValue);
printf("%-22s: %d\n", "Passed value (int)", result);
} else {
// error
}