Example of Interface and Abstract class in real project using C# in ASP.Net

Hi iammann,

Here is a small sample that you can understood the concept.

HTML

<div>
    <table border="0" cellpadding="0" cellspacing="0">
        <tr>
            <td>
                <asp:GridView ID="gvEmployees" runat="server" Caption="<b>Interface</b>" />
            </td>
            <td>
                <asp:GridView ID="gvCustomers" runat="server" Caption="<b>Abstract</b>" />
            </td>
        </tr>
    </table>
</div>

For interface create a property class with the name Employees

/// <summary>
/// Employees get set property.
/// </summary>
public class Employees
{
    public string EmployeeId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

Then create interface IEmployee

/// <summary>
/// interface IEmployee.
/// </summary>
public interface IEmployee
{
    /// <summary>
    /// Get list of Employees.
    /// </summary>
    /// <returns>List of Employees</returns>
    List<Employees> PopulateEmployees();
}

Then create class Employee which inherit interface.

/// <summary>
/// Employee Class inherits IEmployee interface.
/// </summary>
public class Employee : IEmployee
{
    /// <summary>
    /// Get list of Employees.
    /// </summary>
    /// <returns>List of Employees</returns>
    public List<Employees> PopulateEmployees()
    {
        string strConnString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        SqlConnection con = new SqlConnection(strConnString);
        string query = "SELECT TOP 10 [EmployeeID],[LastName],[FirstName] FROM [Employees]";
        SqlCommand cmd = new SqlCommand(query);
        SqlDataAdapter sda = new SqlDataAdapter(cmd);
        cmd.Connection = con;
        DataTable dt = new DataTable();
        sda.Fill(dt);
        List<Employees> employees = new List<Employees>();
        foreach (DataRow row in dt.Rows)
        {
            employees.Add(new Employees
            {
                EmployeeId = row["EmployeeId"].ToString(),
                FirstName = row["FirstName"].ToString(),
                LastName = row["LastName"].ToString()
            });
        }
        return employees;
    }
}

For abstract same way create class with the name Customer

/// <summary>
/// Summary description for Customer
/// </summary>
public abstract class Customer
{
    /// <summary>
    /// Gets List of Customers.
    /// </summary>
    /// <returns>List of Customers.</returns>
    abstract public DataTable PopulateCustomers();
}

Create Customers class that override Customer abstract class.

/// <summary>
/// Summary description for Customers
/// </summary>
public class Customers : Customer
{
    /// <summary>
    /// Override PopulateCustomers.
    /// </summary>
    public override DataTable PopulateCustomers()
    {
        string strConnString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        SqlConnection con = new SqlConnection(strConnString);
        string query = "SELECT TOP 10 [CustomerID],[ContactName],[City],[Country] FROM [Customers]";
        SqlCommand cmd = new SqlCommand(query);
        SqlDataAdapter sda = new SqlDataAdapter(cmd);
        cmd.Connection = con;
        DataTable dt = new DataTable();
        sda.Fill(dt);
        return dt;
    }
}

After running the above below is the output.