How to use JNI?

Question

hi all,
i know that pure java can't disable alt+tab,i must use JNI with C language. i have a pile of codes to disable the alt+tab in C but i do not know how to do it in JNI...can anyone help?thanks in advance...
these are my codes in C:
Private Declare Function SystemParametersInfo Lib "user32" _
Alias "SystemParametersInfoA" (ByVal uAction As Long, _
ByVal uParam As Long, lpvParam As Any, ByVal fuWinIni As Long) As Long
Private Const SPI_SCREENSAVERRUNNING = 97
Dim ret As Integer
Dim pOld As Boolean
Private Sub Form_Load()
'The line below calls the function and passes
'the constant and TRUE to fool Windows into thinking
'the screensaver is running and FALSE to do the opposite...
ret = SystemParametersInfo(SPI_SCREENSAVERRUNNING, True, pOld, 0)
End Sub
Private Sub Form_Unload(Cancel As Integer)
'NOTE: THIS MUST BE SET TO FALSE WHEN
'THE FORM OR APP CLOSES
'If you do not set it to false, these keys will not work
'with any app, or with anything in the Windows Environment...
ret = SystemParametersInfo(SPI_SCREENSAVERRUNNING, False, pOld, 0)
End Sub

Answer 1

There really isn't a lot to using JNI.
There are examples on Sun's website:
http://developer.java.sun.com/developer/onlineTraining/Programming/JDCBook/jniexamp.html
There is also a little more simple example at:
http://www.inonit.com/cygwin/jni/helloWorld/java.html
Basically, here are the steps:
1) Create a simple java applet that will call your C/C++ code.
For practise, I would just use the HelloWorld example from www.inonit.com:
package example.jni;
public class HelloWorld {
     private static native void writeHelloWorldToStdout();
     public static void main(String[] args) {
          writeHelloWorldToStdout();
2) Name the file with the code above HelloWorld.java and compile it:
javac HelloWorld.java
3) Use javah to generate the C header file:
javah example.jni.HelloWorld
(You may need to cd to the parent directory of 'example', in this case)
4) The above line should create a example_jni_HelloWorld.h header file.
Use this header file in your C/C++ DLL. Make sure your C/C++ compile knows where to find jni.h. In my compiler, I added the following paths:
C:\J2SDK1.4.1\INCLUDE\
C:\J2SDK1.4.1\INCLUDE\WIN32
5) The trickiest part about JNI is passing in and returning parameters.
If you don't have to pass in or return any parameters, then you're almost done. Replace your C/C++ function protocol with the protocol in the header file you generated. Compile your DLL.
6) Copy the DLL to a path that it will be found by your Java Applet. (If running on Windows, this would be your System32 or System directory.)
7) I also had to edit my Path environment variable to include the Java Runtime bin directory. On my machine it was: C:\J2SDK1.4.1\jre\bin
8) Try running your java applet:
Java example.jni.HelloWorld
Good Luck!