We are using jni.h but its getting errors, please check it this

Question

We are using jni.h but its getting errors, please check it this
Calling from a .dll using Java and JNI - by Borland Developer Support Staff
Abstract:Basic JNI example: making a Win32 API call
Making Native Windows API calls from within a Java Application
One of the main points of Java is to be completely platform independent. However, sometimes it will occur that the developer of an
application will know that his or her application is only going to be run on a specific platform, for example, Win32.
NOTE: This example assumes that you are using JDK 1.2 or later.
Below are the steps for writing a Java application that makes a Win32 API call. The application generates a Swing Jframe and makes it
system modal, or gives it the �Always On Top� functionality, similar to that of the Windows NT Task Manager.
Steps to follow:
1. Write the Java code for the application
2. Run javah.exe on your .class file to generate a C header file
3. write the implementation of your native methods
4. create the shared library
5. run the application
1. Write the Java code for the application
import java.awt.*;
import sun.awt.*;
import sun.awt.windows.*;
import javax.swing.*;
import java.awt.event.*;
public class Frame1 extends JFrame {
int windowHWND = 0;
JButton jButton1 = new JButton();
public Frame1() {
//windowHWND = this.getHwnd();
try {
jbInit();
catch(Exception e) {
e.printStackTrace();
public int getHwnd() {
DrawingSurfaceInfo w = (DrawingSurfaceInfo) ((DrawingSurface) getPeer()).getDrawingSurfaceInfo();
w.lock();
WDrawingSurfaceInfo win32 = (WDrawingSurfaceInfo) w;
int hwnd = win32.getHWnd();
w.unlock();
return hwnd;
static {
System.loadLibrary("windowOnTop");
public static native void WindowAlwaysOnTop(int hwnd, boolean flag);
public static void main(String[] args) {
Frame1 frame11 = new Frame1();
frame11.setSize(400,400);
frame11.setVisible(true);
private void jbInit() throws Exception {
jButton1.setText("jButton1");
this.addWindowListener(new java.awt.event.WindowAdapter() {
public void windowOpened(WindowEvent e) {
this_windowOpened(e);
public void windowClosing(WindowEvent e) {
this_windowClosing(e);
this.getContentPane().add(jButton1, BorderLayout.NORTH);
void this_windowOpened(WindowEvent e) {
windowHWND = this.getHwnd();
System.out.println("the value is: " + this.getHwnd());
this.WindowAlwaysOnTop(windowHWND, true);
void this_windowClosing(WindowEvent e) {
System.exit(0);
Once the code is written, compile it with Jbuilder or the command line javac.exe tool which will result in a generated .class file. You will use
this .class file in the next step.
2. Run javah.exe on your .class file to generate a C header file
The following line represents the basic syntax for running javah.exe:
javah Frame1
where Frame1 is the name of the argument class.
When you run javah.exe, it will generate a header file by the same name as your implementation but with a .h file extension. For this
example the .h file that was generated from the above Java code will be emitted being that it is quite large.
NOTE: Make sure that when you run javah.exe, it is the javah.exe that came with the same JDK that you will be compiling with as there may
be some issues with using a version of javah.exe that is different from that of the JDK you are using to compile.
3. write the implementation of your native methods
Now that you have your Java source and your C header file, it is time to write the implementation of your native methods.
Following is the C code that corresponds to the native methods declared in the Java code listed in step 1:
#include "jni.h"
#include "Frame1.h"
#include <stdio.h>
#include<windows.h>
JNIEXPORT void JNICALL Java_Frame1_WindowAlwaysOnTop(JNIEnv *env, jclass obj, jint hwnd, jboolean flag)
if (flag)
SetWindowPos((HWND) hwnd,HWND_TOPMOST,0,0,0,0,SWP_NOMOVE|SWP_NOSIZE);
else
SetWindowPos((HWND) hwnd,HWND_NOTOPMOST,0,0,0,0,SWP_NOMOVE|SWP_NOSIZE);
return;
You will notice several things: one is that the function signature has �Java_Frame1_� preceeding the name of the function. If there was a
package statement in the Java source, it would appear after ��Frame1_� in the function signature.
Second, you will notice the #include �jni.h�. Normally this would be #include<jni.h>, depending on how you have your libraries set up within
your C compiler.
4. create the shared library
Now you are ready to create the shared library. Using your C compiler, create a .dll file with the code from the C implementation file. Refer
to the doccumentation of the C compiler for details on creating a .dll file.
For those interested in using Borland C++ Builder:
If you have got it installed, you could use Borland C++ Builder 3 or C++ Builder 4 to create your DLL file. If this is the case, you would use
File | New... | DLL C++ Builder will then generate some code for you, and you will just need to add your implementation code to the code
which was generated.
Remember in the Java code in step one there is a line:
static {
System.loadLibrary("windowOnTop");
�windowOnTop� is the name of the .dll file. You can name it whatever you want, just make sure that you specify the appropriate name when
loading the library.
5. run the application
Finally you are ready to run the application. From the command line use java.exe and as the argument specify the name of the class that
you compiled in step one. Once the system loads your DLL, the window that the VM creates should mimic the �Always On Top�
functionality.
We are getting errors like this
�Compiling JNI.H:
Error JNI_MD.H 23: , expected
Error JNI.H 115: Declaration missing
Error JNI.H 200: ) expected
Error JNI.H 202: ) expected

Answer 1

#include "jni.h"
#include "Frame1.h"
#include <stdio.h>
#include<windows.h>
JNIEXPORT void JNICALL Java_Frame1_WindowAlwaysOnTop(JNIEnv *env, jclass obj, jint hwnd, jboolean flag)
if (flag)
SetWindowPos((HWND) hwnd,HWND_TOPMOST,0,0,0,0,SWP_NOMOVE|SWP_NOSIZE);
else
SetWindowPos((HWND) hwnd,HWND_NOTOPMOST,0,0,0,0,SWP_NOMOVE|SWP_NOSIZE);
return;
We are getting errors like this
�Compiling JNI.H:
Error JNI_MD.H 23: , expected
Error JNI.H 115: Declaration missing
Error JNI.H 200: ) expected
Error JNI.H 202: ) expected