帮忙看看这是什么？

Question

java.lang.NullPointerException
org.pan.web.bookclasslist.excute(bookclasslist.java:38)
org.apache.jsp.index_jsp._jspService(index_jsp.java:164)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802
org.pan.web.bookclasslist.excute
我想问一下，这是什么意思，org.pan.web.bookclasslist这是路径还是什么，如果是路径，在哪里指定？

Answer 1

package org.pan.web;import java.sql.*;
import java.util.Vector;
import org.pan.util.*;
import org.pan.web.book.bookclass;/**
 * Title:        图书类别列表
 */public class bookclasslist extends DataBase {
private Vector classlist; //图书类别向量数组

public bookclasslist() throws Exception{
super();
} public Vector getClasslist() {
return classlist;
}
        

public String getSql() {
// sqlStr = "select id,classname from my_Bookclass order by id";
// return sqlStr;
            return "";
} public boolean excute() throws Exception {
int id = 0;
String classname = "";
int rscount = 0;
try {
//rs = stmt.executeQuery(getSql());
rs = stmt.executeQuery("select Id,ClassName from my_Bookclass order by Id");
                        rscount = stmt.getMaxRows();
classlist = new Vector(rscount+1);
classlist.clear();
while (rs.next()){
id = rs.getInt("id");
classname = rs.getString("classname");
bookclass bc = new bookclass(id,classname);
classlist.addElement(bc);
}
rs.close();
return true;
}
catch (SQLException sqle){
System.out.println(sqle);
            return false;
}
}
};这程序不知道为什么一编译就出错，不知道为什么bookclasslist.java:5: package org.pan.util does not exist
import org.pan.util.*;
^
bookclasslist.java:6: package org.pan.web.book does not exist
import org.pan.web.book.bookclass;
                        ^
bookclasslist.java:12: cannot resolve symbol
symbol  : class DataBase
location: class org.pan.web.bookclasslist
public class bookclasslist extends DataBase {
                                   ^
bookclasslist.java:36: cannot resolve symbol
symbol  : variable rs
location: class org.pan.web.bookclasslist
                        rs = stmt.executeQuery("select Id,ClassName from my_Book
class order by Id");
                        ^
bookclasslist.java:36: cannot resolve symbol
symbol  : variable stmt
location: class org.pan.web.bookclasslist
                        rs = stmt.executeQuery("select Id,ClassName from my_Book
class order by Id");
                             ^
bookclasslist.java:37: cannot resolve symbol
symbol  : variable stmt
location: class org.pan.web.bookclasslist
                        rscount = stmt.getMaxRows();
                                  ^
bookclasslist.java:40: cannot resolve symbol
symbol  : variable rs
location: class org.pan.web.bookclasslist
                        while (rs.next()){
                               ^
bookclasslist.java:41: cannot resolve symbol
symbol  : variable rs
location: class org.pan.web.bookclasslist
                                id = rs.getInt("id");
                                     ^
bookclasslist.java:42: cannot resolve symbol
symbol  : variable rs
location: class org.pan.web.bookclasslist
                                classname = rs.getString("classname");
                                            ^
bookclasslist.java:43: cannot resolve symbol
symbol  : class bookclass
location: class org.pan.web.bookclasslist
                                bookclass bc = new bookclass(id,classname);
                                ^
bookclasslist.java:43: cannot resolve symbol
symbol  : class bookclass
location: class org.pan.web.bookclasslist
                                bookclass bc = new bookclass(id,classname);
                                                   ^
bookclasslist.java:46: cannot resolve symbol
symbol  : variable rs
location: class org.pan.web.bookclasslist
                        rs.close();
                        ^
12 errors