jni CallStaticLongMethod always return 0L

Issue

I have a static method in a Java class called getCurrValue()

package com.my;
public class MyClass {
    public static long value = 5L;
    public static long getCurrValue(){
        return value;
    }
}

and I have a method in native c/c++ code called useValue(JNIEnv* env). When I try to use the Java static method getCurrValue() to get the value in native c/c++ code , I always get 0L as result - why?

void useValue(JNIEnv* env) {
    jclass clazz = env->FindClass("com/my/MyClass");
    jlong result = -1L;
    jmethodID get_curr_value_method_id = env->GetStaticMethodID(clazz,"getCurrValue","()J");
    result = env->CallStaticLongMethod(clazz,get_curr_value_method_id);
    // the result is 0L
}

Solution

I tested this code in a native method and on my Nexus 9 with Android 6.0 and it's working perfectly.

jstring Java_it_stefanocappa_ndkexample_Example_stringFromJNI( JNIEnv* env, jobject thiz ) {    
    jclass clazz = (*env)->GetObjectClass(env, thiz);        
    jmethodID staticMethodId1;
    staticMethodId1 = (*env)->GetStaticMethodID(env, clazz, "getCurrValue", "()J");
    jlong staticMethodResult2;
    staticMethodResult2 = (jlong) (*env)->CallStaticLongMethod(env, clazz, staticMethodId1);
    return (*env)->NewStringUTF(env, "Hello from JNI);
}

If you are not satisfied about my answer, please write and i'll post the entire fully-working example ;)

---

Update as suggested:

I updated a project on Github that i realized some months ago.

Repository: https://github.com/Ks89/NdkExample_AndroidStudio

Look "example.c" lines 155-166.

Obviously, in this example there are also other features.

Answered By - Stefano Cappa