/////////////////////////////////////////////////////////////////
//
// MessageBoxTest.java
//

/**
 * Demonstrate JDirect, JNI and RNI calls.
 * @author Jonathan Locke
 */

public class MessageBoxTest
{
    static boolean isJNISupported;
    static boolean isRNISupported;
    static boolean isJDirectSupported;

    /** @dll.import("USER32") */
    static native void MessageBox(int hwndOwner, String text, 
                                  String title, int fuStyle);
    /**
     * Package parameters and call the Win32 message box directly through 
     * J/Direct 
     * @param title Title of message box 
     * @param message The message to show 
     */
    
    static void messageBox(String title, String message)
    {
        MessageBox(0, message, title, 0);
    }

    /**
     * Main application entrypoint.
     * @param arg Command line arguments
     */
    
    static public void main(String[] arg)
    {
        // JNI is not currently supported in the Microsoft VM. Conversely, 
        // RNI, COM and J/Direct are not supported in the JDK's VM.
        String vendor = System.getProperty("java.vendor").toLowerCase();

        isRNISupported     = vendor.indexOf("microsoft") != -1;
        isJDirectSupported = isRNISupported;
        isJNISupported     = !isRNISupported;

        String message = "Brought to you by the letter 'J'.";

        if (isJDirectSupported)
        {
            messageBox("JDirectMessageBox", message);
        }

        if (isJNISupported)
        {
            JNIMessageBox.messageBox("JNIMessageBox", message);
        }

        if (isRNISupported)
        {
            RNIMessageBox.messageBox("RNIMessageBox", message);
        }
    }
}

Figure 2   JNIMessageBox

 /* DO NOT EDIT THIS FILE - it is machine generated */
 #include <jni.h>
 /* Header for class JNIMessageBox */
 
 #ifndef _Included_JNIMessageBox
 #define _Included_JNIMessageBox
 #ifdef __cplusplus
 extern "C" {
 #endif
 /*
  * Class:     JNIMessageBox
  * Method:    messageBox
  * Signature: (Ljava/lang/String;Ljava/lang/String;)V
  */
 JNIEXPORT void JNICALL Java_JNIMessageBox_messageBox
   (JNIEnv *, jclass, jstring, jstring);
 
 #ifdef __cplusplus
 }
 #endif
 #endif

Figure 3   JNIMessageBox.cpp

 /////////////////////////////////////////////////////////////////
 //
 // JNIMessageBox.cpp
 //
 
 #define STRICT
 #pragma warning(disable: 4201)  // Nameless struct/union
 #pragma warning(disable: 4514)  // Unreferenced inline function removed
 #include <windows.h>
 #include "JNIMessageBox.h"
 
 extern "C"
 {
 
 ///////////////////////////////////////////////////////////////////////////////
 //
 // @func JNI call to put up a message box
 //
 JNIEXPORT void JNICALL Java_JNIMessageBox_messageBox
 (
  JNIEnv* env,                     // @parm JNI environment pointer
  jclass,                          // @parm Unreferenced
  jstring title,                   // @parm Title of message box
  jstring message                  // @parm Message to display
 )
 {
     jboolean isCopy;
 
     // Use JNI environment pointer to call the appropriate JNI method
     // to get the characters for each string passed in
     const jchar* pwszTitle   = env->GetStringChars(title,   &isCopy);
     const jchar* pwszMessage = env->GetStringChars(message, &isCopy);
 
     // Put up a MessageBox
     ::MessageBoxW(NULL, pwszMessage, pwszTitle, MB_OK);
 
     // Release the character strings 
     env->ReleaseStringChars(title,   pwszTitle);
     env->ReleaseStringChars(message, pwszMessage);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 //
 // @mfunc entrypoint to dynamic link library
 // @rdesc non-zero on success, zero on failure
 //
 __declspec(dllexport) BOOL WINAPI DllMain 
 (
  HINSTANCE,                     // @Parm Instance handle of dll
  DWORD,                         // @Parm Reason for call to DllMain
  LPVOID                         // @Parm reserved
 )
 {
     return TRUE;
 }
 
 } // extern "C"

Figure 4   RNIMessageBox.java

/////////////////////////////////////////////////////////////////
//
// RNIMessageBox.java
//

public class RNIMessageBox
{
    static native void messageBox(String title, String message);
    static
    {
        System.loadLibrary("RNIMessageBox");
    }
}

///////////////////////////////// End of File /////////////////////////////////
 
/*  DO NOT EDIT - automatically generated by msjavah  */
#include <native.h>
#pragma warning(disable:4510)
#pragma warning(disable:4512)
#pragma warning(disable:4610)

struct Classjava_lang_String;
#define Hjava_lang_String Classjava_lang_String

/*  Header for class RNIMessageBox  */

#ifndef _Included_RNIMessageBox
#define _Included_RNIMessageBox

#define HRNIMessageBox ClassRNIMessageBox
typedef struct ClassRNIMessageBox {
#include <pshpack4.h>
    long MSReserved;
#include <poppack.h>
} ClassRNIMessageBox;

typedef struct ClassArrayOfRNIMessageBox {
    int32_t MSReserved;
    const unsigned long length;
    HRNIMessageBox * const body[1];
} ClassArrayOfRNIMessageBox;
#define HArrayOfRNIMessageBox ClassArrayOfRNIMessageBox
#define ArrayOfRNIMessageBox ClassArrayOfRNIMessageBox

#ifdef __cplusplus
extern "C" {
#endif
__declspec(dllexport) void __cdecl RNIMessageBox_messageBox (
    struct HRNIMessageBox *, struct Hjava_lang_String *, 
    struct Hjava_lang_String *);
#ifdef __cplusplus
}
#endif

#endif  /* _Included_RNIMessageBox */

#pragma warning(default:4510)
#pragma warning(default:4512)
#pragma warning(default:4610)

/////////////////////////////////////////////////////////////////
//
// RNIMessageBox.cpp
//

#define STRICT
#pragma warning(disable: 4201)  // Nameless struct/union
#pragma warning(disable: 4514)  // Unreferenced inline function removed
#include <windows.h>
#include <native.h>
#include "RNIMessageBox.h"

extern "C"
{
    
///////////////////////////////////////////////////////////////////////////////
//
// @func Gets the version of RNI that this library was built against
// @rdesc RNIVER value when the library was statically linked together
//
__declspec(dllexport) DWORD __cdecl RNIGetCompatibleVersion()
{
    return RNIVER;
}

///////////////////////////////////////////////////////////////////////////////
//
// @func Static method that puts up a message box
// @rdesc 
//
__declspec(dllexport) void __cdecl RNIMessageBox_messageBox
(
 struct HRNIMessageBox*,            // @Parm NULL instance variable
 struct Hjava_lang_String* title,   // @Parm Title of message box
 struct Hjava_lang_String* message  // @Parm Message to show
)
{
    MessageBoxW(0, javaStringStart(message), javaStringStart(title), MB_OK);
}

} // extern "C"

///////////////////////////////// End of File /////////////////////////////////