A simple JNI example

Tested on centos 5.8

Step 1: declare a native function in the Java source file

public class AddMe{        static {                System.loadLibrary("hello");        }        public native void sum(int a, int b);        public static void main(String[] args){                AddMe am = new AddMe();                am.sum(2, 5);        }}

Step 2: Compile the Java class

javac AddMe.java

Step 3: generate the C header file

javah -jni AddMe

You will find the "addme. H" file in the current working directory

Step 4: implement the C function "sum" (by JNI naming convention the function name wocould be java_addme_sum)

We create a C source file called "addme. c"

#include "AddMe.h"#include <stdio.h>JNIEXPORT void JNICALL Java_AddMe_sum (JNIEnv *env, jobject obj, jint a, jint b){        jint result = 0;        result = a + b;        printf("hello world %d\n", result);}

Step 5: Compile the C code and generate a share library "libhello. So" (it must have the name libhello so that system. loadlibrary ("hello") can dynamically load the Library)

gcc -fPIC -I/usr/lib/jvm/java/include -o libhello.so -shared ./addme.c

Step 6: run the Java bytecode

java -Djava.library.path=. AddMe

Then you can see "Hell world 7" printed on Console