JNI - Java Native Interface

The Java Native Interface (JNI) is a programming framework that allows Java code running in the Java virtual machine (VM) to call and be called by native applications (programs specific to a hardware and operating system platform) and libraries written in other languages, such as C, C++ and assembly.
... from the link

HelloWorld.java

class HelloWorld
{
    public native int[][] multiply(int A[][], int B[][]);
    static
    {
        System.loadLibrary("HelloWorldImp");
    }

    public static void main(String[] args)
    {
        HelloWorld test = new HelloWorld();
        int[][] A = new int[5][5];
        int[][] B = new int[5][5];
        int[][] result = test.multiply(A, B);
        System.out.println(result[0][0]);
    }
}

然後使用 javac HelloWorld.java 產生出 HelloWorld.class
接下來再使用 javah HelloWorld 產生出 HelloWorld.h

HelloWorld.h

/* DO NOT EDIT THIS FILE - it is machine generated */

#ifndef __HelloWorld__
#define __HelloWorld__

#include 

#ifdef __cplusplus
extern "C"
{
#endif

JNIEXPORT jobjectArray JNICALL Java_HelloWorld_multiply (JNIEnv *env, jobject, jobjectArray, jobjectArray);

#ifdef __cplusplus
}
#endif

#endif /* __HelloWorld__ */

再把 HelloWorld.c 寫出來
HelloWorld.c

#include "HelloWorld.h"

JNIEXPORT jobjectArray JNICALL Java_HelloWorld_multiply (JNIEnv *env, jobject obj, jobjectArray A, jobjectArray B);
{
    jobjectArray C;
    ...
    return C;
}

最後使用 gcc -Wall -g -shared -fPIC HelloWorld.c -o libHelloWorldImp.so
現在終於可以執行 Java 程式了
java -Djava.library.path=./ HelloWorld
使用 Java 來做跨平台程式開發
在關鍵部份再利用 JNI 來將平台特性最佳化