session监听器HttpSessionListener接口获得在线用户运行出错,帮忙看看,该怎么解决

session监听器HttpSessionListener接口获得在线用户运行出错,帮忙看看
//hello类
package   lognumber;

import   javax.servlet.http.HttpSessionEvent;
import   javax.servlet.http.HttpSessionListener;

public     class   hello   implements   HttpSessionListener   {
        String   name;
        public   hello(String   name){
                this.name=name;
        }
        public   String   getName()   {
          return   name;
  }
  public   void   setName(String   name)   {
          this.name   =   name;
  }
        public   void   sessionCreated(HttpSessionEvent   se)   {
                test.add(name);
        }

       
        public   void   sessionDestroyed(HttpSessionEvent   se)   {
                test.delete(name);
        }
}


//test类
package   lognumber;
import   java.util.ArrayList;
public   class   test   {
      static   ArrayList   list=new   ArrayList();
        public   static   void   add(String   name){//   添加用户
                list.add(name);
        }
        public   static   void   delete(String   name){//删除用户
                list.remove(name);
        }
        public   static   ArrayList   getName(){
                return   list;
        }
       
}

//Servlet1

package   lognumber;

import   javax.servlet.*;
import   javax.servlet.http.*;
import   java.io.*;
import   java.util.*;
import   lognumber.*;
public   class   Servlet1   extends   HttpServlet   {
        private   static   final   String   CONTENT_TYPE   =   "text/html;   charset=GBK ";

        //Initialize   global   variables
        public   void   init()   throws   ServletException   {
        }

        //Process   the   HTTP   Get   request
        public   void   doGet(HttpServletRequest   request,   HttpServletResponse   response)   throws
                        ServletException,   IOException   {
                response.setContentType(CONTENT_TYPE);
                PrintWriter   out   =   response.getWriter();
                request.setCharacterEncoding( "gbk ");
                String   name   =   request.getParameter( "name ");

                hello   he=new   hello(name);
              ArrayList   list=test.getName();
                out.println( "当前在线用户 ");
                for   (int   i   =   0;   i   <   list.size();   i++)   {
                        out.println(list.get(i));
                }
        }
        //Process   the   HTTP   Post   request
        public   void   doPost(HttpServletRequest   request,   HttpServletResponse   response)   throws
                        ServletException,   IOException   {
                doGet(request,   response);
        }

        //Clean   up   resources
        public   void   destroy()   {
        }
}
//XML配置
<?xml   version= "1.0 "   encoding= "UTF-8 "?>
<web-app   xmlns= "http://java.sun.com/xml/ns/j2ee "   xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance "   xsi:schemaLocation= "http://java.sun.com/xml/ns/j2ee   http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd "   version= "2.4 ">
    <display-name> WebModule1 </display-name>
    <listener>
        <listener-class> lognumber.hello </listener-class>
    </listener>
    <servlet>
        <servlet-name> servlet1 </servlet-name>
        <servlet-class> lognumber.Servlet1 </servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name> servlet1 </servlet-name>
        <url-pattern> /servlet1 </url-pattern>
    </servlet-mapping>
</web-app>


//刚一运行就提示
严重:   Error   configuring   application   listener   of   class   lognumber.hello
java.lang.InstantiationException:   lognumber.hello
at   java.lang.Class.newInstance0(Class.java:335)
at   java.lang.Class.newInstance(Class.java:303)
at   org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3618)
at   org.apache.catalina.core.StandardContext.start(StandardContext.java:4104)
at   org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1012)
at   org.apache.catalina.core.StandardHost.start(StandardHost.java:718)
at   org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1012)
at   org.apache.catalina.core.StandardEngine.start(StandardEngine.java:442)
at   org.apache.catalina.core.StandardService.start(StandardService.java:450)
at   org.apache.catalina.core.StandardServer.start(StandardServer.java:683)
at   org.apache.catalina.startup.Catalina.start(Catalina.java:537)
at   sun.reflect.NativeMethodAccessorImpl.invoke0(Native   Method)
at   sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

at   sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at   java.lang.reflect.Method.invoke(Method.java:585)
at   org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:271)
at   org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:409)
2007-4-2   22:39:53   org.apache.catalina.core.StandardContext   listenerStart
严重:   Skipped   installing   application   listeners   due   to   previous   error(s)
2007-4-2   22:39:53   org.apache.catalina.core.StandardContext   start
严重:   Error   listenerStart
2007-4-2   22:39:53   org.apache.catalina.core.StandardContext   start
严重:   Context   [/WebModule1]   startup   failed   due   to   previous   errors


[解决办法]
当应用程序试图使用 Class 类中的 newInstance 方法创建一个类的实例，而指定的类对象因为是一个接口或是一个抽象类而无法实例化时，抛出该异常。
[解决办法]
我觉得是hello这个类没有默认的构造方法
public hello(){
this.name= " ";
}
把这个构造方法加里,看看