Time for action – calling back Java from native code

Let's continue our Store by calling back the interface we defined from native code:

1. In com_packtpub_store_Store.cpp, declare method descriptors with type jmethodID for each callback, which is going to be cached:

   ...
   static Store gStore;
   
   static jclass StringClass;
   static jclass ColorClass;
   
   static jmethodID MethodOnSuccessInt;
   static jmethodID MethodOnSuccessString;
   static jmethodID MethodOnSuccessColor;
   ...

2. Then, cache all the callback descriptors in JNI_OnLoad(). This can be done in two main steps:

   Getting a Class descriptor with the JNI method FindClass(). One can find a class descriptor, thanks to its absolute package path, here: com./packtpub/store/Store.

   Retrieving a method descriptor from the class descriptor with GetMethodID(). To differentiate several overloaded methods, the signatures retrieved earlier with javap must be specified:

   ...
   JNIEXPORT jint JNI_OnLoad(JavaVM* pVM, void* reserved) {
       JNIEnv *env;
       if (pVM->GetEnv...