What is the right way to store a java object in a native class?

I need to store a java object inside a native class. But i have this problem:

java side:

package com.gabrik.gabos;

public class Main {
static {
    System.loadLibrary("JniTest");
}

public static void main(String[] args) throws Exception {
    saveCar(new Car("my car"));
    System.out.println("saved");
    System.out.println(getSavedCar().getName());
}

public static native void saveCar(Car car);

public static native Car getSavedCar();

public static class Car {
    private String name;

    public Car(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}
}

com_gabrik_gabos_Main.h:

#include <jni.h>
/* Header for class com_gabrik_gabos_Main */

#ifndef _Included_com_gabrik_gabos_Main
#define _Included_com_gabrik_gabos_Main
#ifdef __cplusplus
extern "C" {
#endif

extern jobject car;

/*
* Class:     com_gabrik_gabos_Main
* Method:    saveCar
* Signature: (Lcom/gabrik/gabos/Main/Car;)V
*/
JNIEXPORT void JNICALL Java_com_gabrik_gabos_Main_saveCar
(JNIEnv *, jclass, jobject);

/*
* Class:     com_gabrik_gabos_Main
* Method:    getSavedCar
* Signature: ()Lcom/gabrik/gabos/Main/Car;
*/
JNIEXPORT jobject JNICALL Java_com_gabrik_gabos_Main_getSavedCar
(JNIEnv *, jclass);

#ifdef __cplusplus
}
#endif
#endif

com_gabrik_gabos_Main.cpp:

#include "pch.h"
#include "com_gabrik_gabos_Main.h"

jobject car = nullptr;

JNIEXPORT void JNICALL Java_com_gabrik_gabos_Main_saveCar
(JNIEnv* env, jclass cls, jobject value) {
    car = value;
}

JNIEXPORT jobject JNICALL Java_com_gabrik_gabos_Main_getSavedCar
(JNIEnv* env, jclass cls) {
    return car;
}

logs:

saved
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x0000016e427709d7, pid=21724, tid=0x0000000000002930
#
# JRE version: Java(TM) SE Runtime Environment (8.0_301-b09) (build 1.8.0_301-b09)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (25.301-b09 mixed mode windows-amd64 compressed oops)
# Problematic frame:
# v  ~StubRoutines::atomic_cmpxchg_long
#
# Failed to write core dump. Minidumps are not enabled by default on client versions of Windows
#
# An error report file with more information is saved as:
# C:\Users\user\IdeaProjects\GabOS\hs_err_pid21724.log
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.java.com/bugreport/crash.jsp
#

Why the when i pass the Car object to the saveCar, the jobject pointing to the car stops working once the method exits? because as you saw, the next time i use the jobject which was pointing to the car, now points to $h1t. What am i doing wrong?