import java.sql.*; 

import javax.swing.JOptionPane;

public class ConnectDB{ 
    public void connectData() 
    { 
        Connection con = null;
        Statement st = null;
        try
        { 
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); 
            String url="jdbc:odbc:Driver={MicroSoft Access Driver             (*.mdb)};DBQ=E:\\EclipseWS\\AddressList\\source\\DB.mdb"; 
            con = DriverManager.getConnection(url,"amin","admin"); 
            st = con.createStatement();  //如何把这个获得的st传给同一工程下的另外一个
                                                            //类login,ResultSet rs = st.excuteQuery("");
                                                    //来获取数据库的用户名。
        }catch(Exception ex)
            { 
              JOptionPane.showMessageDialog(null , "数据库连接错误"+"SQL exception:" + ex.getMessage() , "Error" , JOptionPane.ERROR_MESSAGE);
            } 
    
    } 
}

import java.sql.*; 

import javax.swing.JOptionPane;

public class ConnectDB{ 
    private Connection con=null;
    private Statement st=null;
    public void connectData() 
    { 
      
        try
        { 
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); 
            String url="jdbc:odbc:Driver={MicroSoft Access Driver             (*.mdb)};DBQ=E:\\EclipseWS\\AddressList\\source\\DB.mdb"; 
            con = DriverManager.getConnection(url,"amin","admin"); 
            st = con.createStatement();  //如何把这个获得的st传给同一工程下的另外一个
                                                            //类login,ResultSet rs = st.excuteQuery("");
                                                    //来获取数据库的用户名。
        }catch(Exception ex)
            { 
              JOptionPane.showMessageDialog(null , "数据库连接错误"+"SQL exception:" + ex.getMessage() , "Error" , JOptionPane.ERROR_MESSAGE);
            } 
    
    } 
   public statement getSt(){
     return st;
       
   }
}
[code=Java]

------解决方案--------------------
可以用个简单的工厂模式
Java code

public class ConnectDB{ 
    private Connection con=null;
    private Statement st=null;
    private String url;
    static {
        Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); 
        url="jdbc:odbc:Driver={MicroSoft Access Driver             (*.mdb)};DBQ=E:\\EclipseWS\\AddressList\\source\\DB.mdb"; 
    
    }

    public static Connection createConnection() 
    { 
      
        try
        { 
            con = DriverManager.getConnection(url,"amin","admin"); 
            return con

        }catch(Exception ex)
            { 
              JOptionPane.showMessageDialog(null , "数据库连接错误"+"SQL exception:" + ex.getMessage() , "Error" , JOptionPane.ERROR_MESSAGE);
            } 
    
    } 
}