IPv4 vs. IPv6 programming question

Question

I have a machine that I believe is running only IPv6 and here is why, when I try to compile and run this example I found on the internet:
import java.net.*;
import java.io.*;
public class ip
public static void main ( String[] args ) throws IOException
String hostname;
BufferedReader input = new BufferedReader ( new InputStreamReader(System.in) );
System.out.print("\n");
System.out.print("Host name: ");
hostname = input.readLine();
try
InetAddress ipaddress = InetAddress.getByName(hostname);
System.out.println("IP address: " + ipaddress.getHostAddress());
catch ( UnknownHostException e )
System.out.println("Could not find IP address for: " + hostname);
When I run the example and type in liveupdate.symantec.com I get this from the program:
Host name: liveupdate.symantec.com
Could not find IP address for: liveupdate.symantec.com
If I run it like this java –Djava.net.preferIPv4Stack=true ip I get the following results:
Host name: liveupdate.symantec.com
IP address: 207.148.159.25
Can someone here help explain what the system property java.net.preferIPv4Stack=true means? And which way should I change the code so that it will work without having to set this system property?
Thank you very much for your time

Answer 1

... and it's crossposted there. Locking this thread.