Java developers

Java newbie here.. just started learning it (crashcourse) this summer at my job (consisting of programming in java...)

i'm still not acquainted with too many of Javas errors/bugs and how to fix them. I was looking for a bit more help than the impersonal documentation.

What should I look for with a Java.lang.NullPointerException error? I know the basics, but feel free to review them again if you wish. I've reviewed the particular function/method that is in error, and I know I'm missing something. More information is available upon request!

Thanks a lot you guys! :o)

Here is some source for a command line version of a java client. Didn't add in hardly any functionality, was just testing some HTTP specific JavaAPI stuff. It works, and i guess that is the important part. If anyone wants some commenting, or if you want to take it any hack it and want some help, lemme know. -ken (P.s. I'm almost done with the full gui (Swing) based livejournal Client) I'll drop a note here when its ready for download.

/* Command line jLiveJournal
 * 2001 Sevensoft (Ken Brooks)
 *
 * GPL License, blah blah blah.
 *
 * This is about as basic as you can make a livejournal client.
 * There is no formatting of the LiveJournal server response.
 * I didn't add in another cl argument for subject, but feel free.
 *
 */

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

public class Jlj {
    public static void main(String[] args) throws Exception {

	String modeString = new String("");

	if(args.length == 3)
		// should have usename password "post message"
	{
		String usernameString = args[0];
		String passwordString = args[1];
		String postStringFromArg = URLEncoder.encode(args[2]);

		Calendar calendar = new GregorianCalendar();

		modeString = "mode=postevent&user=" + usernameString +
					 "&password=" + passwordString +
					 "&event=" + postStringFromArg +
					 "&year=" + calendar.get(Calendar.YEAR) +
					 "&mon="  + (calendar.get(Calendar.MONTH)+1) +
					 "&day="  + calendar.get(Calendar.DATE) +
					 "&hour=" + calendar.get(Calendar.HOUR_OF_DAY) +
					 "&min="  + calendar.get(Calendar.MINUTE);
	}
	else if(args.length == 2)
		// should have username password
	{
		String usernameString = args[0];
		String passwordString = args[1];
		modeString = "mode=login&user=" + usernameString + "&password=" + passwordString;
	}
	else
	{
		System.out.println("Usage:");
		System.out.println("  loginMode:  ");
		System.out.println("  postMode :   \"Post message\"");
	}


	URL url = new URL("http://www.livejournal.com/cgi-bin/log.cgi");
	HttpURLConnection connection = (HttpURLConnection)url.openConnection();
	connection.setRequestMethod("POST");
	connection.setRequestProperty("Host", "www.livejournal.com");
	connection.setRequestProperty("Content-type", "application/x-www-form-urlencoded");
	connection.setRequestProperty("Content-length", Integer.toString(modeString.length()));
	connection.setDoOutput(true);

	PrintWriter out = new PrintWriter(
                              connection.getOutputStream());

	out.print(modeString);

	out.close();
	System.out.println(connection.getResponseCode());

	BufferedReader in = new BufferedReader(
				new InputStreamReader(
				connection.getInputStream()));
	String inputLine;

	while ((inputLine = in.readLine()) != null)
	    System.out.println(inputLine);

	in.close();
    }
}