Writing a Java Program with Native Methods

environment: Ubuntu 16.04.1 LTS (GNU/Linux 4.4.0-31-generic x86_64), JDK 1.8.0_101
  • Hello.java
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public class Hello {
    public static native int add(int x, int y);
    static{
        System.loadLibrary("hello");
    }
    public static void main(String[] args){
        System.out.println(Hello.add(233, 344));
    }
}
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$ javac Hello.java
$ javah -jni Hello
  • Hello.h
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/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class Hello */
#ifndef _Included_Hello
#define _Included_Hello
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     Hello
 * Method:    add
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_Hello_add
  (JNIEnv *, jclass, jint, jint);
#ifdef __cplusplus
}
#endif
#endif
  • HelloImpl.c
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#include <stdio.h>
#include <jni.h>
#include "Hello.h"
JNIEXPORT jint JNICALL Java_Hello_add
(JNIEnv *env, jclass clazz, jint x, jint y) {
    return x + y;
}
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$ gcc -shared -I/$JAVA_HOME/include -I/$JAVA_HOME/include/linux -fPIC HelloImpl.c -o libhello.so
$ export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:`pwd`
$ java Hello