Use of Partial Class.,.

using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        A a = new A();
        string ss = a.msg("umapathi");
        Response.Write(ss);
        string s2 = a.msg1("second");
        Response.Write(s2);
    }
}

public partial class A
{
 

    public string msg(string m)
    {
        return "first class";
    }
}

public partial class A
{
    public string msg1(string mm)
    {
        return "second class";
    }

}