InetAddress localhost = InetAddress.getLocalHost();

// this code assumes IPv4 is used

byte[] ip = localhost.getAddress();

for (int i = 1; i <= 254; i++) {

ip[3] = (byte)i;
InetAddress address = InetAddress.getByAddress(ip);
if (address.isReachable(1000))
{
    // machine is turned on and can be pinged
}
else if (!address.getHostAddress().equals(address.getHostName())
{
    // machine is known in a DNS lookup
}
else
{
    // the host address and host name are equal, meaning the host name could not be resolved
}

}

It takes too much time to find Ip addresses connected to LAN I have 100 PCS in Lan it takes 9 minutes so its is time consuming and i want display it in the Jcombobox so please give me the fastest way thanks and regards Nilesh Gawade

may be u can make it using Thread each Thread control over a limited range such as 10 0-9 and make array of Thread ........ use it.

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.imageio.*;
import javax.swing.*;
import java.io.*;
import java.awt.image.*;
import java.net.*;




public class NetScanner implements Runnable
{
    String str;
    int nub;

    public NetScanner(String str,int nub)
    {
        this.str = str; 
        this.nub = nub;
    }
/*  
    public void checkHost()
    {
        for(int i=0; i<256;i++)
        {
            if(IntelAddress.getByName(str+"."+i).isReachable(1000))
                System.out.println("host"+str+"."+i+"is connected");
        }

    }
*/
    public void run ()
    {
        try
        {
        for(int i=nub; i<nub+10;i++)
        {

        System.out.println(".......");
        System.out.println(str);
        System.out.println(nub);
            if(InetAddress.getByName(str+"."+i).isReachable(1000))
                System.out.println("host"+str+"."+i+"is connected");
        }
        }
        catch(Exception e){System.out.println(e);}
    }
    public static void main(String []args)
    {
        //System.out.println("give subnet");
        //Scanner out = new Scanner(System.in);
        //NetScanner n = new NetScanner(out.next());
        Thread t[] = new Thread[25];
        for(int i=0; i<25;i++)
        {
            t[i] = new Thread(new NetScanner("10.124.168",i*10));
        }
        for(int i=0; i<25;i++)
        {
            t[i].start();
        }

    }

}

u may check it i m not conformed but it may work