Get Started with JNI

Step 1: Create a Java test file JNITest.java

public class JNITest {
    public native void printString();

    static {
        System.loadLibrary("printstr");
    }   

    public void print() {
        printString();
    }   

    public static void main(String args[]) {
        (new JNITest()).print();
    }   
}

Step 2: Compile the Java file and generate a header file JNITest.h

$javac JNITest.java
$javah -jni JNITest

Step 3: Create a C test file printstr.c

#include <stdio.h>
#include <jni.h>
#include "JNITest.h"

JNIEXPORT void JNICALL Java_JNITest_printString (JNIEnv* env, jobject obj)
{
    printf("Hello, World!\n");
}

Step 4: Compile C file to produce the native lib "libprintstr.jnilib"

$gcc -dynamiclib -o libprintstr.jnilib -I/System/Library/Frameworks/JavaVM.framework/Headers printstr.c -framework JavaVM

Step 5: Run the Java test, which would show "Hello World!"

$java JNITest