Jump to content
  • Advertisement


This topic is now archived and is closed to further replies.


Java/C++ Integration

This topic is 5227 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hello, I''ve been messing around with the idea of using a C++/Java conglomerate in my next big project. The idea is using C++ for the processor intensive stuff, and Java for the rest. Basically, my C++ program spawns a JVM and interfaces with it through the JNI interface. Anyway, I was wondering if anyone had any resources to the JNI stuff other than what''s on SUN''s site. I can''t seem to find anything solid as far as spawning a JVM inside a C++ program, just little tidbits here and there. One thing that''s really bothering me so far, is that I couldn''t find the library for my little test program to link against. By trial and error I found that linking with libgcj worked as expected, but I don''t think this is the way that it''s meant to be. Just so it''s clear what I''m taking about, here''s a paste of my little test program. Thanks, Kevin
//C++ program that uses a Java program to calculate the pth prime for all primes less than 60000

#include <iostream>
#include <jni.h>

using namespace std;

int main() {
  JavaVM *jvm;
  JNIEnv *env;
  if (JNI_CreateJavaVM(&jvm, (void**)&env, 0) == JNI_ERR) {
    cout << "Error creating java vm" << endl;
  } else {
    jclass cls = env->FindClass("Test");
    jmethodID mid = env->GetStaticMethodID(cls, "test", "(I)I");
    cout << "What prime would you like ";
    int p;
    cin >> p;
    cout << "The " << p << "th prime is: " 
	 << env->CallStaticIntMethod(cls, mid, p)
	 << endl;

import java.util.*;

public class Test {
    public static int test(int pr) {
	int[] primes = new int[60000];
	for(int j=0; j<60000; ++j)
	    primes[j] = j % 2;
	primes[2] = 1;
	for(int j=3; j<60000; j+=2)
	    if (primes[j] == 1)
		for(int k=j+j; k<60000; k+=j)
		    primes[k] = 0;
	for(int j=0, cnt=0; j<60000; ++j)
	    if (primes[j] == 1)
		if (cnt == pr)
		    return j;
	return 0;

	javac Test.java
	g++ -o javaincpp javaincpp.cpp -Wall -O2 -lgcj # I shouldn''t have to link against libgcj should I?

	rm -f javaincpp Test.class

Share this post

Link to post
Share on other sites
I think you have to link against libjava; it''s in the SDK somewhere.

libgcj is the gnu compiler for Java. It includes a JVM which can run bytecode too (dunno if it has a JIT; it definitely has an interpreter).

gcj is the gnu compiler for Java - it makes .java files into native code. There is a class library too (although it''s incomplete at best).

People who think that Java runs too slowly often cite gcj as being better than existing JVMs - because it compiles to native code. This is usually because they measure it by its startup time rather than it actual runtime performance.

Unfortunately, code made with gcj actually runs rather slower than modern JVMs JIT. This is because the JIT actually makes good native code, and gcj does not.

As far as I''m aware, either the library that gcj relies on, or gcj itself, is Unix-specific (that''s to say, there is no Windows port of it).


Share this post

Link to post
Share on other sites
Having said that, I seem to recall that gcj provides the "Java is just another programming language" idiom. There is some way which you can call C++ classes from Java (and vice versa) without having to jump through JNI hoops.

JNI is clumsy and error-prone. I don''t like it.


Share this post

Link to post
Share on other sites

  • Advertisement

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!