1. program Java source file loading Native method
// file name: NativeDemo.java
public class NativeDemo
{
int i;
int j;
public static void main(String args[])
{
NativeDemo ob = new NativeDemo();
ob.i = 10;
ob.j = ob.test();
System.out.println("this is ob.i:"+ob.i+" ");
System.out.println("this is ob.j:"+ob.j);
}
public native int test();
static
{
System.loadLibrary("NativeDemo");
}
}

2.Compile file NativeDemo.java
Javac NativeDemo.java

3.Use javah.exe to produce file NativeDemo.c and NativeDemo.h
a : javah NativeDemo to produce NativeDemo.h which is:
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <native.h>
/* Header for class NativeDemo */

#ifndef _Included_NativeDemo
#define _Included_NativeDemo

#pragma pack(4)

typedef struct ClassNativeDemo {
long i;
long j;
} ClassNativeDemo;
HandleTo(NativeDemo);

#pragma pack()

#ifdef __cplusplus
extern "C" {
#endif
extern long NativeDemo_test(struct HNativeDemo *);
#ifdef __cplusplus
}
#endif
#endif
b : use javah -stubs NativeDemo to produce NativeDemo.c which seems as:
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <StubPreamble.h>

/* Stubs for class NativeDemo */
/* SYMBOL: "NativeDemo/test()I", Java_NativeDemo_test_stub */
__declspec(dllexport) stack_item *Java_NativeDemo_test_stub(stack_item *_P_,struct execenv *_EE_) {
extern long NativeDemo_test(void *);
_P_[0].i = NativeDemo_test(_P_[0].p);
return _P_ + 1;
}
4. Write your own implimentation of method test()
//file name test.c
#include <StubPreamble.h>
#include "nativedemo.h"
#include <stdio.h>

long NativeDemo_test(HNativeDemo *this)
{
printf("hello:! ");
printf("this is in the native method! ");
return (unhand(this)->i)*2;
}

5. link NativeDemo.c and test.c to produce NativeDemo.dll
Use VC++5.0 tools :Cl.exe
Cl /GD NativeDemo.c test.c /LD
then we get NativeDemo.dll


NativeDemo.c
test.c
Generating Code...

/out:NativeDemo.dll
/dll
/implib:NativeDemo.lib
NativeDemo.obj
test.obj
Creating library NativeDemo.lib and object NativeDemo.ex
Press any key to continue




6.Run

java NativeDemo

we get the such result:

D:vj11user ative>java NativeDemo
hello:!
this is in the native method!
this is ob.i:10

this is ob.j:20

D:vj11user ative>


NOTE:
Do not forget this:
c:> set INCLUDE=d:javainclude;d:javawin32;%INCLUDE%
C:>set LIB =d:javalib;%LIB%
where d:java is the directory of your jdk

new version jdk1.2.1 :

With new jdk1.2.1 :

1.javac NativeDemo.java

2. javah NativeDemo to produce head file (You need not to javah -stubs NativeDemo to produce NativeDemo.c file),

You don`t need the c file. Just the NativeDemo.h is sufficient!

3.Use VC++ produce a window dll project and add the NativeDemo.h to it.

then implement the function. All is OK!
NOTE: the data type conversion between java and c++.See jni.h for more information.