Android NDK - JNI findClass returns null

ownClass = (*jniEnv)->FindClass(jniEnv, "com/sample/TestClass");
if(!ownClass )
{
    LOGD("Failed to get ownClass");
}
activityClass = (*jniEnv)->FindClass(jniEnv, "com/sample/MainActivity");
if(!activityClass)
{
    LOGD("Failed to get activityClass");
}

      

        
        
        
      

    

Conclusion: "Failed to get own class"

Both classes are in the same sample package.