public class Student
{
public Student()
{

}

private int _pkid;
private string _name;
private byte _age;
private bool _sex;

public int PKID
{
get{return _pkid;}
set{_pkid=value;}
}

public string Name
{
get{return _name;}
set{_name=value;}
}

public byte Age
{
get{return _age;}
set{_age=value;}
}

public bool Sex
{
get{return _sex;}
set{_sex=value;}
}
}

//没有属性只有公共变量,破坏封装
class A
{
  public int a =0;
}
//没有属性只用方法，繁琐实在繁琐
class B
{
  private int _b;
  public void SetbValue(int b)
  {
    this._b = b;
  }
  public int GetbValue()
  {
    return _b;
  }
}
//使用属性，对于c#3.0版本的还可以这样写，简洁啊
class C
{
   public int c{ get;set;}
}

Class1.cs
private DataTable dt = new DataTable();
public DataTable Dt { get; set; }
    public DataTable GetTable(string sql)
    {
        Class1 c = new Class1();
        SqlConnection cn = Class1.CreateCn();
        SqlDataAdapter da = new SqlDataAdapter(sql, cn);
        da.Fill(c.Dt);
        return c.Dt;
    }

Default.CS
        GridView1.DataSource = c.GetTable("select * from employee");
        GridView1.DataBind();