public class NetInfo {
 public static void main(String[] args) {
    new NetInfo().say();
    }

 public void say() {
   try {
   java.net.InetAddress i = java.net.InetAddress.getLocalHost();
   System.out.println(i);                  // name and IP address
   System.out.println(i.getHostName());    // name
   System.out.println(i.getHostAddress()); // IP address only
   }
   catch(Exception e){e.printStackTrace();}
 }
}

> java NetInfo
realone/209.142.72.112
realone
209.142.72.112

import java.net.*;
import java.util.*;
import java.io.*;
import java.nio.*;

public class IPAdress {
 public void  getInterfaces (){
      try {
         Enumeration e = NetworkInterface.getNetworkInterfaces();

         while(e.hasMoreElements()) {
            NetworkInterface ni = (NetworkInterface) e.nextElement();
            System.out.println("Net interface: "+ni.getName());

            Enumeration e2 = ni.getInetAddresses();

            while (e2.hasMoreElements()){
               InetAddress ip = (InetAddress) e2.nextElement();
               System.out.println("IP address: "+ ip.toString());
            }
         }
      }
      catch (Exception e) {
         e.printStackTrace();
      }
   }

   public static void main(String[] args) {
    IPAdress ip = new IPAdress();
    ip.getInterfaces();
   }
}

> java IPAdress
Net interface: lo
IP address: /127.0.0.1
Net interface: eth0
IP address: /194.168.0.1
Net interface: eth1
IP address: /164.254.147.20
Net interface: ppp0
IP address: /64.68.115.69