大家帮我看一个登陆的servlet吧，它是怎么运作的啊，奇怪啊

由一个LogonServlet，它的perform方法只有一句话，是抛出一个异常，奇怪的是这个程序竟然可以运行，我不知道它怎么进行的逻辑处理，大家见过这样的程序吗LogonServlet.java
package com.futuresoft.monitor.servlets;import java.io.IOException;import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import com.futuresoft.monitor.platform.MyBaseServlet;public class LogonServlet extends MyBaseServlet
{ public LogonServlet()
{} public void perform(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException
{
throw new Error("Unresolved compilation problems: \n\tlogusers cannot be resolved\n\tlistener cannot be resolved\n\tSyntax error, insert \"AssignmentOperator Expression\" to complete Expression\n\tservletcontext cannot be resolved\n\tJVM cannot be resolved to a type\n\tSyntax error on token \"monitorexit\", delete this token\n");
}
}
另外MyBaseServlet.java的代码如下// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3) fieldsfirst ansi space 
// Source File Name:   MyBaseServlet.javapackage com.futuresoft.monitor.platform;import java.io.IOException;
import java.io.UnsupportedEncodingException;import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import com.futuresoft.monitor.user.CheckAvailable;public class MyBaseServlet extends HttpServlet
{ private static final String CONTENT_TYPE="text/html; charset=gb2312"; public MyBaseServlet()
{} public void init() throws ServletException
{} public void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException
{
response.setContentType("text/html; charset=gb2312");
try
{
request.setCharacterEncoding("gb2312");
} catch (UnsupportedEncodingException e)
{
request.setAttribute("info","编码转换失败...");
forward(request,response,"/err.jsp");
return;
}
if (!CheckAvailable.checkSessionAvailable(request))
{
request.setAttribute("info","session 失效...");
forward(request,response,"/err.jsp");
return;
} else
{
perform(request,response);
return;
}
} public void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException
{
response.setContentType("text/html; charset=gb2312");
System.out.println(request.getParameter("logonname"));
System.out.println(request.getParameter("logonpw"));
try
{
request.setCharacterEncoding("gb2312");
} catch (UnsupportedEncodingException e)
{
request.setAttribute("info","编码转换失败...");
forward(request,response,"/err.jsp");
return;
}
if (!CheckAvailable.checkSessionAvailable(request))
{
request.setAttribute("info","session 失效...");
forward(request,response,"/err.jsp");
return;
} else
{
perform(request,response);
return;
}
} public void perform(HttpServletRequest httpservletrequest1,HttpServletResponse httpservletresponse1) throws ServletException,IOException
{} public void forward(HttpServletRequest request,HttpServletResponse response,String url) throws ServletException,IOException
{
ServletContext sc=getServletContext();
RequestDispatcher rd=sc.getRequestDispatcher(url);
rd.forward(request,response);
} public void destroy()
{}
}