NetBeans中导入Access问题

import java.sql.*;
//连接数据库
public class Database {
    private Statement stmt = null;
    ResultSet rs = null;
    private Connection conn = null;
    String sql;
    String strurl = "jdbc:odbc:scmanage";

    public Database(){
    }

    //打开数据库连接
    public void OpenConn() throws Exception{
        try{
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
            conn = DriverManager.getConnection(strurl);
        }
        catch(Exception e){
            System.err.println("OpenConn:"+e.getMessage());
        }
    }

    //执行sql语句，返回结果集rs
    public ResultSet executeQuery(String sql){
        stmt = null;
        rs = null;
        try{
            stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
            rs = stmt.executeQuery(sql);
        }
        catch(SQLException e){
            System.err.println("executeQuery:"+e.getMessage());
        }
        return rs;
    }

    //执行sql语句
    public void executeUpdate(String sql){
        stmt = null;
        rs = null;
        try{
            stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
            stmt.executeQuery(sql);
            conn.commit();
        }
        catch(SQLException e){
            System.err.println("executeUpdate:"+e.getMessage());
        }
    }

    public void closeStmt(){
        try{
            stmt.close();
        }
        catch(SQLException e){
            System.err.println("closeStmt:"+e.getMessage());
        }
    }

    //关闭数据库连接
    public void closeConn(){
        try{
            conn.close();
        }
        catch(SQLException ex){
            System.err.println("aq.closeConn:"+ex.getMessage());
        }
    }

    //转换编码
    public static String toGBK(String str){
        try{
            if(str == null)
                str = "";
            else
                str = new String(str.getBytes("ISO-8859-1"),"GBK");
        }
        catch(Exception e){
            System.out.println(e);
        }
        return str;
    }
}

出现了OpenConn:[Microsoft][ODBC 驱动程序管理器] 未发现数据源名称并且未指定默认驱动程序
java.lang.NullPointerException问题
是什么情况？

辛苦 辛苦

补充：Java ,  Eclipse