asked on

How to call the method clearScreen()?

System Information -
1. WindowXP
2. Visual Studio 6 - MS C++ 6.0
3. Java2 Platform, Standard Edition 1.4.2_08 SDK

Please follow my steps and teach me how to fix the problem -
1. Create a Java class named ClearScreen that declares a native method.

class ClearScreen {
public native void clearScreen();

static {
System.loadLibrary("clearscreen");
}

public static void main(String[] args) {
new ClearScreen().clearScreen();
}
}

2. Use javac to compile the Java code

3. Use javah to create a JNI-style header file (a .h file) from the ClearScreen class

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class ClearScreen */

#ifndef _Included_ClearScreen
#define _Included_ClearScreen
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: ClearScreen
* Method: clearScreen
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_ClearScreen_clearScreen
(JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

4. Write the implementation for the native method in a native language (such as ANSI C) source file and saved as ClearScreenImp.c

#include <jni.h>
#include "ClearScreen.h"
#include <stdio.h>
#include <conio.h>

JNIEXPORT void JNICALL
Java_ClearScreen_clearScreen(JNIEnv *env, jobject obj)
{
cls();
return o;
}

Now, I have the clearscreen.dll, clearscreen.lib, ClearScreenImp.obj, ClearScreen.class ...
My question is how can I call this clearScreen() within my java application program?
e.g.

public class Test{

public static void main(String [] args) throws Exception{

System.out.println("Hello World!!!");
// now I want to clear my console, and continue to do something....
// how to invoke the clearScreen() ?
}
}

Thanks

ASKER CERTIFIED SOLUTION

Mick Barry

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bin571

ASKER

hmmmm.......
#include <jni.h>
#include "ClearScreen.h"
#include <stdio.h>
#include <conio.h>

JNIEXPORT void JNICALL
Java_ClearScreen_clearScreen(JNIEnv *env, jobject obj)
{
printf("Hello world");
return o;
}

This one works....so I change the printf("Hello world") to cls(), then it doesn't work :(

#include <jni.h>
#include "ClearScreen.h"
#include <stdio.h>
#include <conio.h>

JNIEXPORT void JNICALL
Java_ClearScreen_clearScreen(JNIEnv *env, jobject obj)
{
cls();
return o;
}

ClearScreenImp.obj: error LNK2001: unresolved external symbol _cls
clearscreen.dll : fatal error LNK1120: 1 unresolved externals.

But, I have compiled the below file successfully before, now I can't compile anymore (got the same error message as above)

#include <stdio.h>
#include <conio.h>
void main (void){
clrscr();
return 0;
}

Any idea?

Mick Barry

> ClearScreenImp.obj: error LNK2001: unresolved external symbol _cls

Thats saying you haven't told the linker where to find cls.

> now I can't compile anymore (got the same error message as above)

Have you changed the command you use to compile/link

bin571

ASKER

I didn't change anything, but I uninstalled the j2ee and installed the j2se. Then, set the path (j2se).
I haven't changed anything about the visual C++ :(

SOLUTION

ashok3sep

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bin571

ASKER

I have gone through all the steps. But now, I can't even compile the file like -

#include <stdio.h>
#include <conio.h>
void main (void){
clrscr();
return 0;
}

e.g cl try.c

but I don't have any problem to compile this file before :(

ashok3sep

since you have uninstalled java you have to again link the JNI.h and an another file jni_md.h to the c file

ashok3sep

also say the c file where to look for the conio.h and stdio.h header files.

then compile it and should work for you.

Mick Barry

its not having a problem with compiling, its the linking that is having the problem.

bin571

ASKER

the thing is I rewrited a simple c file named abc.c

#include <stdio.h>
#include <conio.h>
void main (void){
clrscr();
return 0;
}

and compiled this file c:\ cl abc.c
I can't even compile abc.c!!!

ashok3sep

have you set the PATH variable correctly

you can do that and check for it.

set PATH = c:\compiler Directory\bin;

ashok3sep

Follow the link below to create a dll of a c program that lijks to your Java program and hope this helps you

http://www.functionx.com/visualc/libraries/win32dll.htm

SOLUTION

Mayank S

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