JNI how to access Java Object (Integer)

Question

I have a JNI method to access java method which returns an Integer object. I do not want to return the primitive int type because this code will be modified to handle Generi

Answer 1

You have to invoke the intValue method on the Integer instance to get its primitive value. Use FindClass instead of GetObjectClass (as in your code) to get a reference to the class java.lang.Integer and then GetMethodID and CallObjectMethod to actually invoke the intValue method.

Answer 2

Thanks Jarnbjo,

It works now! This is what I have:

    JNIEXPORT jint JNICALL Java_GenericPeer_print (JNIEnv *jenv, jclass jcls, jobject data){
      jclass peerCls = jenv->GetObjectClass(data);

     jmethodID mGetValue = jenv->GetMethodID(peerCls, "getValue","()Ljava/lang/Integer;");
     if (mGetValue == NULL){
       return(-1);
     }

     jobject value = jenv->CallObjectMethod(data, mGetValue);
     if(value == NULL){
      cout<<"jobject value = NULL"<<endl;
      return(-1);
     }

    //getValue()

     jclass cls = jenv->FindClass("java/lang/Integer");
     if(cls == NULL){
       outFile<<"cannot find FindClass(java/lang/Integer)"<<endl;
     }
       jmethodID getVal = jenv->GetMethodID(cls, "intValue", "()I");
       if(getVal == NULL){
         outFile<<"Couldnot find Int getValue()"<<endl;
       }
       int i = jenv->CallIntMethod(value, getVal);
}