程序如下 如果把ArrayList的声明写在while外面 返回的时候能得到所有人的信息 也就是说数据库里所有人的信息都存到ArrayList声明的al中了    
    public ArrayList getAllPersonInfm()
    {
[color=FF0000]        ArrayList al = new ArrayList();[/color]
        try
        {
            //得到链接
            conn = DBToolss.getConnection();
            //得到statement
            state = conn.createStatement();
            String sql = "select * from stuperson";
            rs = state.executeQuery(sql);
            while(rs.next())
            {
                Person p =new Person();
                p.setId(rs.getInt("id"));
                p.setName(rs.getString("name"));
                p.setAddress(rs.getString("address"));
                
                al.add(p);
            }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
        finally
        {
            DBToolss.closeRs(rs);
            DBToolss.closeState(state);
            DBToolss.closeConn(conn);
        }
        return al;
    }
要是按下面这个写法，al在while中声明 为什么只返回一个数据信息呢？
    public ArrayList getAllPersonInfm()
    {
    ArrayList al = null;
        try
        {
            //得到链接
            conn = DBToolss.getConnection();
            //得到statement
            state = conn.createStatement();
            String sql = "select * from stuperson";
            rs = state.executeQuery(sql);
            while(rs.next())
            {
                [color=000080]al = new ArrayList();[/color]
                Person p =new Person();
                p.setId(rs.getInt("id"));
                p.setName(rs.getString("name"));
                p.setAddress(rs.getString("address"));
                
                al.add(p);
            }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
        finally
        {
            DBToolss.closeRs(rs);
            DBToolss.closeState(state);
            DBToolss.closeConn(conn);
        }
        return al;
    }