Basic Differences between Abstract class and Interface

Behaviour	Abstract Class	Interface
Multiple Inheritance	Not Possible	Possible
Inheritance Chain(of same type)	Possible	Not Possible (does not fall under the inheritance chain of same type)
Concrete Functionality	Possible	Not Possible
Private Members	Not Possible	Possible
Type can be declared as method input parameter	Not Possible (because instance could not be created)	Possible (acceptable with fully implemented instance is being passed)
Structs can implement	Not Possible	Possible
Every member needs to be implemented	No	Yes

We can have the interface as the input type for some method which accepts only the objects which completely implements this interface. Following example shows this:


<asp:Button id="Button1" runat="server" OnClick="Goooooogle"/>





public partial class TestViewState_Default : System.Web.UI.Page
{




protected void Goooooogle(object sender, EventArgs e)
    {
        myClass myclass = new myClass();
        DoSomeAction(myclass);
    }


    private void DoSomeAction(myInterface myinterface)
    {
        Response.Write(myinterface.myfield.ToString());
    }


    public class myClass:myInterface
    {
        int _field;
        public int myfield 
        {
            get { return 12; }
            set { _field = value; }
        }


        public int getId()
        {
            return 190;
        }
    }


    public interface myInterface
    {
       int myfield{get; set;}
       int getId();
    }
}