Hi, I was trying to figure this out. I've been scratching my head all morning and I'm at a mental dead end. Can anyone help me?

Malicious code in red

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package ping;

import java.net.*;
import java.text.SimpleDateFormat;
import java.util.*;

public class PingClient
    private static final int PING_MESSAGES = 10;
    private static final int TOKEN_TIMESTAMP = 2;
    private static final int MAX_WAIT_TIME = 1000;
    private static final String CRLF = "\r\n";

    public static void main(String[] args) throws Exception
        // If user doesn't input both port number and ip address, the program will display an error message.
        if (args.length != 2)
            System.out.println("usage: java PingClient <Host> <Port>");
                System.out.println("\nHost: "+args[1]+"\nIP address: "+args[0]+"\n");
        catch(ArrayIndexOutOfBoundsException e)
            System.out.println("Host name and ip address please");
        byte[] buffer = new byte[1024];  
        //InetAddress host = InetAddress.getByName(args[0]);
        InetAddress host = InetAddress.getByName("localhost");
        int portNumber = Integer.parseInt(args[1]);
        //Create a datagram socket used for sending and recieving UDP packets
       // DatagramSocket socket = new DatagramSocket(new byte[1024],9876,, 1024);
        DatagramSocket socket = new DatagramSocket(buffer, buffer.length);
        //Set up the maximum time the socket waits for responses

        //Construct a ping message to be sent to the Server
        for (int sequence_num = 0; sequence_num < PING_MESSAGES; sequence_num++)
                String message = generatePing(sequence_num);
                DatagramPacket ping_request =
                    new DatagramPacket(message.getBytes(), message.length(), host, portNumber);

                //Send a ping request

                //Datagram packet to hold server response
                DatagramPacket ping_response =
                    new DatagramPacket(new byte[message.length()], message.length());

                //Wait for ping response from server
                catch (SocketTimeoutException e)
                        System.out.println("No response was received from the server");
                catch (Exception e)
                        //Another unknown error may have occured that can't be handled

    private static String generatePing(int sequence_num)
        // For getting current date and time 
        SimpleDateFormat sdfNow = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");
        String strNow = sdfNow.format(new Date(System.currentTimeMillis()));
        return "PING #" + sequence_num + " " + System.currentTimeMillis() + " ("+strNow+")";

    //Print ping page to standard output stream
    private static void printData(DatagramPacket request) throws Exception
        String response = new String(request.getData());
        String[] tokens = response.split(" ");
        //Create sent and received timestamps for RTT
        long sent_timestamp = new Long(tokens[TOKEN_TIMESTAMP]);
        long received_timestamp = System.currentTimeMillis();

        long rtt = received_timestamp - sent_timestamp;

        //Display results
        System.out.print(response+" Received from "+
                request.getAddress().getHostAddress() + " "+"(RTT=" + rtt + "ms)"+CRLF);

you may want to elaborate a bit. what don't you understand about it? what is going wrong?

Study the API documentation for DatagramSocket. It tells you exactly what parameters you can pass to the constructor (neither of yours has a valid parameter list). Judging by the parameters you tried to use, you are probably confusing DatagramSocket and DatagramPacket.