Integrating Java and C++ with GCC/CNI :)

Commands to compile:

#!/bin/bash

# Compile Main for Java bytecode
gcj -C Main.java

# Compile Main for native
gcj -findirect-dispatch -fno-indirect-classes -fpic -c Main.class -o java.o

# Generate header file
gcjh -cp . Main

# Compile C++ file
g++ -fpic -c main.cpp -o main.o

# Link all together
gcc main.o java.o -lstdc++ -lgcj -o prog

main.cpp

// Main headers
#include <cstdlib>
#include <cstdio>
#include <iostream>

// Include the GNU Java runtime
#include <gcj/cni.h>

// Include the Java interface (generated with gcjh!)
#include "Main.h"

// Implement the Java method!
jint Main::sum(jint x, jint y) {
  using namespace std;
  
  cout << "Summing in C++ ;)" << endl;
  
  return x + y;
}

//
int main() {
  using namespace std;
  using namespace java::lang;
  
  JvCreateJavaVM(NULL);
  JvAttachCurrentThread(NULL, NULL);
  
  //JvInitClass(&Main::class$);
  
  Main *m = new Main;
  
  JvDetachCurrentThread();
  
  return EXIT_SUCCESS;  
};

Main.java

public class Main {
  public Main() {
    
    System.out.println("In Java, gonna make a summation... =P");
    
    int r = sum(5, 10);
    
    System.out.printf("Back in Java, Sum of 5 and 10 is %d%n", r);
    
  };
  
  // Mark this method as native, we will implement it in C++ :)
  public native int sum(int x, int y);
};