Superpowered Android JNI: understanding “JNI(jintArray …” format

Question

The Superpowered " Simple USB Example " uses the code below to update the UI on the Java side based on a C++ method. This is the first time I've seen JNI alone followed by a method. I've seen JNIEXPORT in similar situations, but not just JNI . I'd like to learn more about this usage but haven't had any luck trying to Google it. Any explanations or references would be appreciated!

C++ Code :

// This is called by the MainActivity Java object periodically.
JNI(jintArray, getLatestMidiMessage, PID)(JNIEnv *env, jobject __unused obj) {
    jintArray ints = env->NewIntArray(4);
    jint *i = env->GetIntArrayElements(ints, NULL);
    pthread_mutex_lock(&mutex);
    i[0] = latestMidiCommand;
    i[1] = latestMidiChannel;
    i[2] = latestMidiNumber;
    i[3] = latestMidiValue;
    pthread_mutex_unlock(&mutex);
    env->ReleaseIntArrayElements(ints, i, NULL);
    return ints;
}

Java code :

 // Update UI every 40 ms.
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                int[] midi = getLatestMidiMessage();
                switch (midi[0]) {
                    case 8: textView.setText(String.format(Locale.ENGLISH, "Note Off, CH %d, %d, %d", midi[1] + 1, midi[2], midi[3])); break;
                    case 9: textView.setText(String.format(Locale.ENGLISH, "Note On, CH %d, %d, %d", midi[1] + 1, midi[2], midi[3])); break;
                    case 11: textView.setText(String.format(Locale.ENGLISH, "Control Change, CH %d, %d, %d", midi[1] + 1, midi[2], midi[3])); break;
                }
                handler.postDelayed(this, 40);
            }
        };
        handler = new Handler();
        handler.postDelayed(runnable, 40);
    }

Answer 1

Look at the code in that example:

// Beautifying the ugly Java-C++ bridge (JNI) with these macros.
#define PID com_superpowered_simpleusb_SuperpoweredUSBAudio // Java package name and class name. Don't forget to update when you copy this code.
#define MAKE_JNI_FUNCTION(r, n, p) extern "C" JNIEXPORT r JNICALL Java_ ## p ## _ ## n
#define JNI(r, n, p) MAKE_JNI_FUNCTION(r, n, p)

He's using some macro magic to make things "cleaner". In reality it makes it less wordy but far harder to understand, and production code should never have stuff like this.