Getting network download(bytes receive per second) and uploadspeed(bytes send per second) with Hyperic Sigar

Question

I recently added some external jar file from hyperic sigar, name log4j.jar and sigar.jar. The purpose is to get the system(Operating System)'s download(bytes receive per second) and uploadspeed(bytes send per second) speed like 40 kb/s or 1.3 kb/s for a system in developing to monitor the computers performance.

I run across some of the classes in this library like NetInterfaceStat that have function such as NetInterfaceStat.getRxBytes and NetInterfaceStat.getTxBytes. However i believe that NetInterfaceStat class need some initialization/constructor.

Could anyone teach me how to initialize this class? Here is a example of my code.. Im developing on Mac Osx Snow Leopard and Windows 7

package pack;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.*;
import java.util.Map.Entry;
import java.lang.management.*;
import org.hyperic.sigar.*;

public class systemMonitor extends Thread {
    private static Sigar sigar;
    NetInterfaceStat netstat;
    boolean truefalse=true;
public void run(){

try{

Thread.sleep(5000);
sigar = new Sigar();
System.out.print("System Monitor Started\n");
netstat = sigar.getNetInterfaceStat("en1");
System.out.print(sigar.getNetInterfaceList().toString());
}
catch(Exception e){
    System.out.print(e);
}

while(truefalse){

if(data.firstExecution!=true){
    try{
        System.out.print(netstat.getRxBytes()+" "+netstat.getTxBytes());
    }
    catch(Exception e){
    System.out.print(e);
    break;
    }
}
}
}

Im sorry if i did not provide any detailed information^^ some external links to my question... http://www.hyperic.com/support/docs/sigar/

also i found a almost similar thread in the forum too, but lack of informations... Sigar network speed