How to speed up my code?

[fuser]

Hey folks, recently I wrote a small application in java where it generates ip addresses in a 192.168.x.x block, and then proceeds to ping them to see if the address is available or not.

The main issue with it right now is that it's extremely slow when I tested it in a network, and so sometimes it takes 10 minutes just to finish up an address beginning with 192.168.1.x, before proceeding with the following block.

I'm still unclear on multithreading, so I was wondering if anyone here can show me how to implement it into my code.

Here's my code:

import java.io.*;
import java.net.*;
import java.net.InetAddress;

public class pingBlock
{
	public static void main(String args[])
	{
		int oct1, oct2;
		
		for(oct1 = 1; oct1 <=255; oct1++)
		{
			for(oct2 = 1; oct2 <=255; oct2++)
			try
		{
			InetAddress address = InetAddress.getByName(String.format("192.168.%d.%d", oct1, oct2));
			boolean reachable = address.isReachable(1000);

			System.out.println("Addr: " + address.getHostAddress());
       		System.out.println("Reach: " + address.isReachable(3000));
    	}
    		catch (UnknownHostException e)
    		{
    			System.out.println("unable to look up IP Address block");
    		}
			catch (IOException e)
			{
				System.out.println("unable to look up IP Address block");
			}
		}
	
	}
}

[NormR1]

How long does it take if you manually ping an address?
The timeout is (1+3) seconds, so (255*4)/60 = 16+ minutes

Add some debugging code to printout the System currentTimeMillis to see how long each "ping" takes.

[fuser]

ok, how do I do that? I'm afraid I don't really know how to add the debugging code part.

[NormR1]

Its very simple. Add the following at various points in the code where you want to see the values of variables.
Use System.outprintln("var=" + var); // show the value of var

For timings use something like the following:

long beginTest = System.currentTimeMillis();
           .... body of testing code here
      System.out.println("test took=" + (System.currentTimeMillis() - beginTest));   //test took=9969

[fuser]

actually, I'm still not clear on how to do this, on how to add the variables and at where should I place the timing for the code.

I haven't done this before, so I'm still unclear how to get it done.