Example JNI/C++ Hello World in Ubuntu

HelloJNI.java

public class HelloJNI {
    static {
        System.loadLibrary("hello");    // load libhello.so
    }

    private native void sayHello();

    public static void main(String[] args) {
        new HelloJNI().sayHello();
    }
}

HelloJNIImpl.cpp

#include <iostream>
#include <jni.h>
#include "HelloJNI.h"   // auto-generated by `javah HelloJNI`

using namespace std;

JNIEXPORT void JNICALL Java_HelloJNI_sayHello (JNIEnv *, jobject) {
    cout << "Hello world. My name is Roboss" << endl;
    return;
}

makerun.md

export JAVA_INC=/usr/lib/jvm/java-8-oracle/include

Step 1: compile the .class file and auto-generate a .h header file

javac -h . HelloJNI.java

Step 2: make the shared library with the name linked in said Java source, and implementing said native method

g++ -std=c++11 -shared -fPIC -I$JAVA_INC -I$JAVA_INC/linux HelloJNIImpl.cpp -o libhello.so

Step 3: run JVM with java.library.path set to include said shared library

java -Djava.library.path=. HelloJNI

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