ASP.NET

  <asp:DataList ID="DataList1" runat="server" RepeatColumns="2" Width="50px"
       DataKeyField="category" EnableViewState="False">
      <ItemTemplate>
  <br />
  <h2>
  <asp:Label ID="Label1" runat="server">
<a id="anchor1" runat="server" href='<%# "Directory/Default.aspx?id="+ Eval("cate_id")%>'>
    <%# Eval("category") %>
    </a>
    </asp:Label>
  </h2>
  </ItemTemplate>
  </asp:DataList>

1. In class, Abstract method has no body but Virtual method has body.
2. Abstract method can be declared in Abstract class only but there is no need of Abstract class for Virtual method.
3. Abstract method must be override in Derived class but Virtual method may be override or not.
4. Abstract method is also called Pure Virtual Method
5. Abstract method must be declared in Abstract class, we did not create an object of Abstract class.

using System;
namespace LearnProject
{

    abstract class TestClassA
    {
          public void Method1()
        {
            Console.WriteLine("I am in Method1() of TestClassA ");
        }
          public virtual void Method2()
          {
              Console.WriteLine("I am in Method2() of TestClassA ");
          }

          public abstract void Method3();

    }

    class TestClassB : TestClassA
    {
        public  override void Method2()
        {
            Console.WriteLine("I am in Method2() of TestClassB ");
        }

        public override void Method3()
        {
            Console.WriteLine("I am in Method3() of TestClassB ");
        }
    }

    class Abstract_and_Virtual_methods
    {
        public static  void Main()
        {

            TestClassB testClassB = new TestClassB();
            testClassB.Method1();
            testClassB.Method2();
            testClassB.Method3();

            TestClassA testClassA = new TestClassB();
            testClassB.Method1();
            testClassA.Method2();
            testClassA.Method3();

            // TestClassB b = new TestClassA() is not allowed

            TestClassB b = new TestClassB(); 
            b = testClassB; // Object of TestClassB is assigned

            b = testClassA as TestClassB; //  Here We need type cast 

            Console.Read();
        }
    }
}