Win a copy of Microservices Testing (Live Project) this week in the Spring forum!
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other Pie Elite all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Tim Cooke
  • Ron McLeod
  • Jeanne Boyarsky
  • Paul Clapham
Sheriffs:
  • Liutauras Vilda
  • Henry Wong
  • Devaka Cooray
Saloon Keepers:
  • Tim Moores
  • Stephan van Hulst
  • Tim Holloway
  • Al Hobbs
  • Carey Brown
Bartenders:
  • Piet Souris
  • Mikalai Zaikin
  • Himai Minh

How to use native

 
Ranch Hand
Posts: 270
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hi,
Could someone give me an example on how to use native methods?
class A{
native void method();
}
How and where should I implement method(), such that I can run the code above?
I hope I am not being vague..
Thanks.
 
Ranch Hand
Posts: 504
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Write native methods contains step-by-step instructions to write and run native methods.
 
Cathy Song
Ranch Hand
Posts: 270
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Thanks Vad. That article was very helpful.
 
Vad Fogel
Ranch Hand
Posts: 504
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Cathy, I tried to follow the instructions, but fell short because -stubs flag errors out due to the JNI specs.
Maybe, that article was outdated. I found Sun Tutorial: Native Methods. -stubs is not mentioned there. Wonder if we can accomplish it?
 
Ranch Hand
Posts: 330
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hello. I tried out the native methods using the following steps:

1. Create the java file MyFirstNativeImplementation.java:
public class MyFirstNativeImplementation {
static {
System.loadLibrary("NativeTest");
}
public native int getLesserNumber(int x, int y);
public static void main(String[] args){
MyFirstNativeImplementation myfirstnative = new MyFirstNativeImplementation();
System.out.println(myfirstnative.getLesserNumber(4,5)); // parameters to pass to the native method
}
}
** "NativeTest" is the C++ dll file containing the native method you will create.
2. Compile the java class file: javac MyFirstNativeImplementation.java
3. Create the c++ header file using: javah <class file name> (without the 'class' extension)
** MyFirstNativeImplementation.h is created after executing the command.
4. header file contains the new method signature to use in your c++ program:
JNIEXPORT jint JNICALL Java_MyFirstNativeImplementation_getLesserNumber
(JNIEnv *, jobject, jint, jint);

5. Create your c++ program using the method signature defined in the header file:
a. I wrote the ff. code using Visual Studio .NET. The code is shown below.
Using .NET, I only had to write the last method in the code below.

In your C++ Project, add the existing jni.h file which can be found in your
<JAVA_HOME>\include folder.

You will also need to include directories to your C++ project. In the
.NET menu...Tools..Options...Projects, click on VC++ Directories and
include the following directories:

<JAVA_HOME>\include\win32
<JAVA_HOME>\include
<the directory where MyFirstNativeImplementation.h is located>


Dont forget to include the header file MyFirstNativeImplementation.h
#include "stdafx.h"
#include "NativeTest.h"
#include "MyFirstNativeImplementation.h"
#ifdef _DEBUG
#define new DEBUG_NEW
#endif

BEGIN_MESSAGE_MAP(CNativeTestApp, CWinApp)
END_MESSAGE_MAP()

CNativeTestApp::CNativeTestApp()
{}
CNativeTestApp theApp;

BOOL CNativeTestApp::InitInstance()
{
CWinApp::InitInstance();
return TRUE;
}
JNIEXPORT jint JNICALL Java_MyFirstNativeImplementation_getLesserNumber
(JNIEnv *, jobject, jint x, jint y) {

int result = 0;

if (x < y)
result = x;
if (y < x)
result = y;
return result;
}

b. Build the C++ solution. .NET menu..Build...Build Solution

6. Execute your MyFirstNativeImplementation java file using:
java -Djava.library.path="<directory where your dll is located>" MyFirstNativeImplementation
I'm not really a C++ programmer and I dont know if there is a simplier way. I hope this helps.
 
Seriously? That's what you're going with? I prefer this tiny ad:
Free, earth friendly heat - from the CodeRanch trailboss
https://www.kickstarter.com/projects/paulwheaton/free-heat
reply
    Bookmark Topic Watch Topic
  • New Topic