Convert JNI types to Native types

You just need to cast jintto int using C style casts. Same for jboolean to bool (if you're using C99 bool type) or to uint8_t (if you're using std int types) or to unsigned char.

Open $NDK_ROOT/platforms/android-8/arch-arm/usr/include/jni.h and you'll see jint, jboolean etc are just typedefs.

To cast a jboolean (which may only contain the values JNI_FALSE or JNI_TRUE) to a native bool I would use something like this :

(bool)(jboolean == JNI_TRUE)

If perhaps the jboolean isn't coming from the JVM, then testing for jboolean != JNI_FALSE might be considered safer.