Java programming with Java Native Interface ( JNI ) / Calling Native C functions from JAVA using JNI

JAVA and JNI
pre-requisite – Install Java SE Development Kit 6u14 under /usr/jdk1.6.0_14
Write a JAVA class [ HelloWorld.java ]

public class HelloWorld { 
static { 
System.loadLibrary("hello"); 
} 
public native void printHelloWorld();
}


Compile the class using javac

sudo javac HelloWorld.java

after this HelloWorld.class file should get created.
Create header file required for writing a native program

sudo javah -jni HelloWorld

Write a helloworld.c native c program.

#include "HelloWorld.h"
#include <stdio.h>
JNIEXPORT void JNICALL
Java_HelloWorld_printHelloWorld (JNIEnv *env, jobject obj) { printf("Hello Worldn");
}


Create a shared library.

gcc -I/usr/jdk1.6.0_14/include -I/usr/jdk1.6.0_14/include/linux -shared -o libhello.so HelloWorld.c

Write a Main java class[ Main.java ], which will call native function.

public class Main { 
public static void main(String[] args) { 
new HelloWorld().printHelloWorld(); 
}
}


Compile Main.java

javac Main.java

Run the program

java Main

Reference’s
1) Using the JAVA Native interface’s
2) JNI Example
3) Integrating Native methods into Java
4) Imp- Introduction to JNI
5) http://java.sun.com/docs/books/jni/html/start.html

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