http status 500 error in tomcat 6 while using eclipse helios

  package com.lala.servlets;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class LoginServlet extends HttpServlet{
    public void init(ServletConfig sc){
        System.out.println("init() login servlet");
    }
    public void service(HttpServletRequest req,HttpServletResponse res)throws IOException,ServletException{
        System.out.println("service() login servlet");
        String un=req.getParameter("username");
        String pw=req.getParameter("password");
        String msg=" ";
        if(un.equals(pw)){
            msg="Hello"+un+"!your login is sucessful";
        }else{
            msg="hello"+un+"!your login failed";
        }
        res.setContentType("text/html");
        PrintWriter out=res.getWriter();
        System.out.println("<fontsize=6 color=red>"+msg+"<font>");
    }
    public void destroy(){
        System.out.println("destroy() login servlet");
    }
}

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

java.lang.NullPointerException com.lala.servlets.LoginServlet.service(LoginServlet.java:14) javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

Dec 26, 2012 1:16:18 PM org.apache.catalina.core.StandardWrapperValve invoke SEVERE: Servlet.service() for servlet LoginServlet threw exception java.lang.NullPointerException at com.lala.servlets.LoginServlet.service(LoginServlet.java:14) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454) at java.lang.Thread.run(Unknown Source)