java.lang.NullPointer.Exception错误
编译通过,运行出现这个错误
import java.sql.*;

public class conn
{
private String driver= "sun.jdbc.odbc.JdbcOdbcDriver ";
private String url= "jdbc:odbc:huang ";//
private String user= "abc ";
private String password= "123 ";//softrunhnccc
private Connection conn=null;
private ResultSet rs=null;
private Statement stmt=null;

public conn()
{
try
{
Class.forName(driver);
try {
conn = DriverManager.getConnection(url, user, password);
stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE);
}
catch (SQLException ex) {
System.out.println(ex.getMessage());
}
}
catch(java.lang.ClassNotFoundException e)
{
System.err.println( "Class Loading Exception: "+e.getMessage());
}
}

public ResultSet executeQuery(String sql) //query
{
try
{
rs=stmt.executeQuery(sql);
}
catch(SQLException ex)
{
System.err.println( "Query Exception: "+ex.getMessage());

// System.err.println( "SQL: "+sql);
}
return rs;
}

public int executeUpdate(String sql) //insert,delete,update
{
int i=0;
try
{
i=stmt.executeUpdate(sql);
}
catch(SQLException ex)

另外,我的另一段代码出现同样的错误,调用了这个文件
import java.util.*;
import conn;
public class test1
{



public static void main(String[] args)
{

for(int i=1;i <30;i++)
for(int j=1;j <i;j++)
{
Insert(i,j);
}
// conn1.close();
}
public static int Insert(int pathIdNumber,int offsetNumber)
{
Random r=new Random();
conn conn2=new conn();
int rows=0;
String a1=String.valueOf(r.nextInt(2));
String a2=String.valueOf(r.nextInt(9));
String a3=String.valueOf(r.nextInt(9));
String b1=String.valueOf(r.nextInt(2));
String b2=String.valueOf(r.nextInt(9));
String b3=String.valueOf(r.nextInt(9));
String c1=String.valueOf(r.nextInt(2));
String c2=String.valueOf(r.nextInt(9));
String c3=String.valueOf(r.nextInt(9));

String d1=String.valueOf(r.nextInt(2));
String d2=String.valueOf(r.nextInt(9));
String d3=String.valueOf(r.nextInt(9));
String ip=a1+a2+a3+ ". "+b1+b2+b3+ ". "+c1+c2+c3+ ". "+d1+d2+d3;
String sql= "insert into path(pathid,offset,ip) values( "+pathIdNumber+ ", "+offsetNumber+ ", ' "+ip+ " ') ";
rows+=conn2.executeUpdate(sql);
conn2.close();
return rows;
}
}

[解决办法]
lz，提示NullPointer异常肯定会指出是哪行吧？为什么不贴出来说明呢？
[解决办法]
jf
[解决办法]
仔细看看系统错误信息
System.err.println 等

rs=stmt.executeQuery(sql);
这里 看看sql 是不是空的
或者 你 的连接 conn 是空的