Need to create a "jni-header" ?

Question

Hello,
I'm totally new to JNI, so I read the JNI tutorial and there is said that I need to create a header file based on my java code. Do I always need to do that?
I want to call some functions from a windows dll which is already compiled. Can I load this lib by using "System.loadLibrary(String)" and access its functions by declaring the native methods in my java code?
Regards,
Schlunz

Answer 1

you cannot do that way.
java call of function has different signature
you have to create .h file - go to dos prompt and type
javah -classpath <classpath> <class>
that .h file contane functions in java signature
now write .c or .cpp file, includ there your .h file and compile that as dll
.c file mast contain an implementation of functions whith same signature as in your .h file.
there is example
HelloWorld.java
class HelloWorld {
public native void displayHelloWorld();
static { System.load("c:\\jdk1.3\\bin\\hello.dll");}
public static void main(String[] args) {
new HelloWorld().displayHelloWorld();
HelloWorld.h
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class HelloWorld */
#ifndef IncludedHelloWorld
#define IncludedHelloWorld
#ifdef __cplusplus
extern "C" {
#endif
* Class: HelloWorld
* Method: displayHelloWorld
* Signature: ()V
JNIEXPORT void JNICALL Java_HelloWorld_displayHelloWorld
(JNIEnv *, jobject);
#ifdef __cplusplus
#endif
#endif
HelloWorld.cpp
#include <jni.h>
#include "HelloWorld.h"
#include <stdio.h>
JNIEXPORT void JNICALL
Java_HelloWorld_displayHelloWorld(JNIEnv *env, jobject obj)
printf("Hello world!\n");
return;