樱花煤气灶维修电话:java语言问题，继续回答

代码：
package dbdemo;

import java.sql.*;

public class DB{
public Connection con=null;
public Statement stmt=null;
public ResultSet rs=null;
public String driverStr="org.gjt.mm.mysql.Driver";
public String URLStr="jdbc:mysql://localhost/messagebookdb?user=root&"+
"password=xiaofeng&useUnicode=true";

public DB(){

}

public void executeDB(String sqlStr){
try{
Class.forName("org.gjt.mm.mysql.Driver");

con=DriverManager.getConnection("jdbc:mysql://localhost/messagebookdb?user=root&"+
"password=xiaofeng&useUnicode=true");
stmt=con.createStatement();
rs=stmt.executeQuery(sqlStr);
rs.next();
rs.getInt(1);
}
catch(ClassNotFoundException e1)
{System.out.println("no driver");}
catch(Exception e2)
{System.out.println("bbbbbb");e2.printStackTrace();}
}

public static void main(String a[]){
String str="select * from messagebook";
DB db=new DB();
System.out.println("aaaa");
db.executeDB(str);
}
}

为什么执行的时候说错误。我链接的是mysql数据库。