HelloJNIWorld.java

public class HelloJNIWorld {
        static {
                System.loadLibrary("hellonativeworld");
        }

        static native void helloWorld();

        public static void main(String[] args) {
                helloWorld();
        }
}

libhellonativeworld.c

#include "HelloJNIWorld.h"

JNIEXPORT void JNICALL Java_HelloJNIWorld_helloWorld
  (JNIEnv *env, jclass cls)
{
	puts("Hello native world");
}

Makefile

JAVA_HOME ?= /etc/alternatives/java_sdk
CFLAGS += -I$(JAVA_HOME)/include -I$(JAVA_HOME)/include/linux

all: libhellonativeworld.so

libhellonativeworld.so: libhellonativeworld.c HelloJNIWorld.h

HelloJNIWorld.h: HelloJNIWorld.class

HelloJNIWorld.class: HelloJNIWorld.java

%.so: %.c
	$(CC) $(CFLAGS) $(LDFLAGS) -fPIC -shared -o $@ $<

%.h: %.class
	javah -cp . $(<:.class=)

%.class: %.java
	javac -cp . $<