java操作Sql出现java.lang.NullPointerException错误
我编写了一个java操作sql数据库的类，如下：
package aaa;
import java.sql.*;
public class javaConnectToSql{
Connection conn=null;
/*
*
*String sUrl;//数据库连接字符串
*String sUsername;//数据库登录用户名
*String sPassword;//数据库登录密码
*String sDriver; //数据库驱动名称
*/
//method:连接数据库
public Connection Conn(String sDriver,String sUrl,String sUsername,String sPassword){
try{
Class.forName(sDriver);
Connection conn=DriverManager.getConnection(sUrl,sUsername,sPassword);
}catch(ClassNotFoundException e)//接收连接驱动异常
{
System.out.println( "Driver not found! ");
System.out.println(e.toString());
}catch(SQLException e)//接收sql连接异常
{
System.out.println( "connection data server error! ");
System.out.println(e.toString());
}
return conn;
}
//method:查询数据库，返回结果类型
public ResultSet QuerySql(String sql){
ResultSet rs=null;
Statement stmt=null;
try{
stmt=conn.createStatement();//这个地方出错，第37行
rs=stmt.executeQuery(sql);
}catch(SQLException e){
System.out.println( "222 "+e.toString());
}
return rs;
}
//method:修改数据库，包括添加、删除、修改，返回影响的行数
public int UpdateSql(String sql){
int rs=0;
try{
Statement stmt=conn.createStatement();
rs=stmt.executeUpdate(sql);
}catch(SQLException e){
System.out.println( "333 "+e.toString());
}
return rs;
}
//Close关闭数据库连接
public void Close(){
try{
conn.close();
}catch(Exception e){
System.out.println(e.toString());
}
}
}
然后又编写了一个引用该类的一个类，如下：
package aaa;
import java.sql.*;
public class useSqlClass{
public static void main(String[] args){
useSqlClass usc=new useSqlClass();
javaConnectToSql jcts=new javaConnectToSql();
jcts.Conn( "com.microsoft.jdbc.sqlserver.SQLServerDriver ", "jdbc:microsoft:sqlserver://localhost:1433;databaseName=Northwind ", "sa ", " ");
ResultSet rs1=null;
rs1=jcts.QuerySql( "SELECT * FROM Customers ");//这个地方出错，第9行
try{
while(rs1.next()){
System.out.println(rs1.getString( "CustomerID ")+ " "+rs1.getString( "CompanyName "));
}
}catch(SQLException e){
System.out.println( "111 "+e.toString());
}
}
}
但是运行的时候出现如下错误：
Exception in thread "main " java.lang.NullPointerException
at aaa.javaConnectToSql.QuerySql(javaConnectToSql.java:37)
at aaa.useSqlClass.main(useSqlClass.java:9)
实在是不知道怎么解决了，请教各位大虾！！！
[解决办法]
改一下这个方法：
//method:连接数据库
public Connection Conn(String sDriver,String sUrl,String sUsername,String sPassword){
try{
Class.forName(sDriver);
this.conn=DriverManager.getConnection(sUrl,sUsername,sPassword);
}catch(ClassNotFoundException e)//接收连接驱动异常
{
System.out.println( "Driver not found! ");
System.out.println(e.toString());
}catch(SQLException e)//接收sql连接异常
{
System.out.println( "connection data server error! ");
System.out.println(e.toString());
}
return this.conn;
}
