C++ JNI UnsatisfiedLinkError

Question

I am trying to make a native list in c++ and use it in java, I am fairly sure everything is declared right but I am getting a link error

Java Exception:

Exception in thread "main" java.lang.UnsatisfiedLinkError: Java_List.init_list(Ljava/lang/Object;)J
        at Java_List.init_list(Native Method)
        at Java_List.main(Java_List.java:13)

Java source

public class Java_List
{
    static
    {
        System.loadLibrary("JAVA_JNI_FTC");
    }

    public native long init_list(Object a);

    public static void main(String[] args)
    {
        Java_List list = new Java_List();
        System.out.println(list.init_list(list));
    }

}

header file

#include <jni.h>
#include "List.h"
#include <new>

#ifndef _Included_JAVA_LIST
#define _Included_JAVA_LIST
#ifdef __cplusplus
extern "C" {
#endif
    /*
     * Class:     HelloJNI
     * Method:    sayHello
     * Signature: ()V
     */
    JNIEXPORT jlong JNICALL Java_Java_List_init_list(JNIEnv *, jobject, jobject);
    JNIEXPORT jobject JNICALL Java_Java_List_list_get(JNIEnv *env, jobject thisObj, jint index, jlong list);

#ifdef __cplusplus
}
#endif

typedef struct Java_List Java_List;

struct Java_List
{
    void *list;
    jclass type;
};

void init_Java_List(Java_List *jList, jclass type);
jobject java_list_get(Java_List *jList, int index);
#endif

C ++ source

#include <jni.h>
#include "Java_List.h"  
#include "pch.h"


extern "C"
{
    JNIEXPORT jlong JNICALL Java_Java_List_init_list(JNIEnv *env, jobject thisObj, jobject classType)
    {
        jclass type = env->GetObjectClass(classType);
        Java_List *list = (Java_List *)malloc(sizeof(Java_List));
        init_Java_List(list, type);
        return (jlong)list;
    }

    JNIEXPORT jobject JNICALL Java_Java_List_list_get(JNIEnv *env, jobject thisObj, jint index, jlong list)
    {
        return java_list_get((Java_List *)list, (int)index);
    }
}
/* jni api*/
void init_Java_List(Java_List *jList, jclass type)
{
    jList->list = malloc(sizeof(List<jobject>));
    new (jList->list) List<jobject>();
    jList->type = type;
}

jobject java_list_get(Java_List *jList, int index)
{
    List<jobject> *list = (List<jobject> *) jList->list;
    return *(list->get(index));
}

I am using visual studio for this project, the project builds multiple files not just the dll, I dont know if this the issue. Files

Answer 1

Your Java class name and method name contain underscores, which goes against the naming convention.

If you insist on keeping them, you need to change the name of your C++ function to Java_Java_1List_init_1list. Note the 1s before List and list, which tells the linker to interpret the preceeding underscore as a literal underscore character instead of a naming separator.