[REQUEST]Information about link between C++ trainer and java GUI?

[strontklit]

Hi,

My friend recently developed a C++ trainer for a game and i was planning on creating a nice GUI for it in java language, with dmg calculator and such in it, but also including the trainer...

Now i was hoping to get some tips on what is the best way to link these to together? How should i load the c++ trainer into the GUI?

I've heard i should use .dll files and load that but i am not really sure on how to do that. And ofcourse maybe there are some other ways of doing this?

I hope to get some nice responds containing useful information

Thanks in advance!

[HerrNuebel]

Yes, you should use shared libraries and load them. (JNI)
It's pretty easy but the C++ trainer must be modified or must provide interfaces.
Here's an example using JNI:

// JNITest.java
public class JNITest {
  private native float add(float a, float b);

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

  public static void main(String... args) {
    JNITest test = new JNITest();
    float erg = test.add(12.5f, 5.7f);
    System.out.println(erg);
  }
}

Methods you want to implement in C/C++ must be declared as native.
In static context you load the library. Make sure you only commit the file's name without extension. Java will do that automatically (on Windows systems .dll, on Linux .so).
Now, you can compile that file using java's compiler javac.

javac JNITest.java

If the JNITest.class file was created, you have to use the java tool "javah".

javah -jni JNITest

A C/C++ header file will be created with the following content:

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

#ifndef _Included_JNITest
#define _Included_JNITest
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     JNITest
 * Method:    add
 * Signature: (FF)F
 */
JNIEXPORT jfloat JNICALL Java_JNITest_add
  (JNIEnv *, jobject, jfloat, jfloat);

#ifdef __cplusplus
}
#endif
#endif

As you can see, it's possible to implement that method in both C++ and C.
Let's review the implementation:

#include "JNITest.h"

JNIEXPORT jfloat JNICALL Java_JNITest_add
  (JNIEnv *env, jobject jobj, jfloat a, jfloat b) {
  return a + b;
}

The generated method has more two more parameters:
*env is a pointer to the JVM.
jobj is a reference to the method that called this native code
a and b are our float parameter we want to work with.
After that, you can create your shared library.
I'm using MinGW on Windows:

gcc -shared -Wl,--add-stdcall-alias -I JDK-HOME/include -I JDK-HOME/include/win32 JNITest.cpp -o JNITest.dll

If all files are saved in the same directory, you can run your application with "java JNITest". Otherwise you have to edit the java's library path.

[strontklit]

Thanks this is very usefull information!