I am just speculating here and the title of my post is just based on some tests I performed in my spare time; but, according to them, based on dynamic array lists and strings, Java is far faster than C++.

The simple Java program is this:

package jtest;

import java.util.*;

public class Main
{
        public static void testPtrList(int z)
        {
                ArrayList<String> list = new ArrayList<String>();
                int z0 = z * 2000;
                for (int i = z0; i < z0 + 2000; i++)
                {
                  String s = "X-";
                  s += i;
                  list.add(s);
                }
        }
	
        public static void main(String... args)
        {
                long t0 = System.currentTimeMillis();
		
                for (int i = 0; i < 10000; i++)
                {
                  if (i % 1000 == 0) System.out.println(i);	  
                  testPtrList(i);
                }
		
                long tz = System.currentTimeMillis();
                System.out.println("Milliseconds: " + (tz - t0));
        }
}

As you can see, the test is quite simple, calls a method 10000 times and the method creates 2000 strings and adds them into a dynamic array list.

I also implemented the same stuff using STL in C++:

#include <string>
#include <vector>
#include <iostream>

using namespace std;

void testList(int i)
{
  char aux[10];
  
  int z0 = i * 2000;
  vector<string> v;
  for (int i = z0; i < z0 + 2000; i++)
  {
    string s("X-");
    sprintf(aux, "%d", i);
    s += aux;
    v.push_back(s);
  }
}

int main()
{
  for (int i = 0; i < 10000; i++)
  {
    if (i % 1000 == 0) printf("%d\n", i);
    
    testList(i);   
  }
  return 0;
}

The results:

In my box, the C++ program is executed in 15 seconds approximately, but the program executed using the HotSpot JVM, is executed in….

in…

2 SECONDS!!!

I know my test is tiny and it cannot be useful as a real world performance benchmark, but it says some interesting things:

• There are things where Java outperforms C++ with almost no effort.
• I implemented the C++ thing using STL; I have also created my own String and Array classes [as optimized as I could] and implemented the same test using them: the performance was similar. My classes were implemented using full pointers [trying to mimic the Java behavior]. So, I think the problem is not in the code, but in the compiler.
• I replaced g++ to llvm-g++ and the C++ program was executed in about 10 seconds [33% faster than the g++ binary].
• I implemented a similar thing in C# and tested using Mono, but the thing got executed in 21 seconds; so, Mono is behind Java right now; I have no environment to run such C# program using the .NET Framework [and running it inside a virtual machine is not fair at all], so I cannot infer anything about this.
  No matter if the performance is inferior in other areas, my simple test demonstrates the amazing development of the Java JIT compiler.

Ah! I have also compiled my Java program using gcj [to native code]…. and the execution took 30 seconds approx… so… gcj is behind Java right now too.