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See edit for latest problem. I am trying to pass a Vector3 value from my cpp library to my java activity. I am able to do it vice versa, but cannot seem to find a way to go cpp to java. Anyone mine helping me out with this? I am receving this error: undefined reference to 'jni_createjavavm'

JavaVM *jvm; /* denotes a Java VM */
JNIEnv *env; /* pointer to native method interface */
JavaVMInitArgs vm_args; /* JDK/JRE 6 VM initialization arguments */
JavaVMOption* options = new JavaVMOption[1];
options[0].optionString = "-Djava.class.path=/usr/lib/java";
vm_args.version = JNI_VERSION_1_6;
vm_args.nOptions = 1;
vm_args.options = options;
vm_args.ignoreUnrecognized = false;
/* load and initialize a Java VM, return a JNI interface
 * pointer in env */
JNI_CreateJavaVM(&jvm, &env, &vm_args);
delete options;
/* invoke the Main.test method using the JNI */
jclass cls = env->FindClass("MenuActivity");
jmethodID mid = env->GetStaticMethodID(cls, "Test", "(I)V");
env->CallStaticVoidMethod(cls, mid);
/* We are done. */
jvm->DestroyJavaVM();

Nov 11 2018 @2031 UTC+9 | EDIT: New Problem.. Crashes with java_class == NULL.

JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void *reserved) 
//Some Other Code Not Regarding JVM

JNIEnv *env;
vm->AttachCurrentThread(&env, NULL);
jclass cls = env->FindClass("MenuActivity");
jmethodID mid = env->GetStaticMethodID(cls, "Test", "(I)V");
env->CallStaticVoidMethod(cls, mid);
return JNI_VERSION_1_6;

On Android, there is no JNI_CreateJavaVM(). The apps run in JVM which is essential to access system APIs and services.

The callbacks from native code to the Java part of the app use the JNIEnv * that must belong to the current thread.

If this runs on a Java thread, the JNIEnv is received as the first parameter by the native method. You can call back to Java from a native thread, too. But then, you must attach the thread to JVM. AttachCurrentThread() accepts JavaVM * which can be stored as a global in your native code. You can obtain it in JNI_OnLoad() or derive it from JNIEnv with GetJavaVM().

Each native thread that is attached, must be detached on termination. The best practice is to use pthread_key_create() to define a destructor function that will be called before the thread exits.

You can read more explanations in the Android JNI tips article.