An abstract class contains abstract members which define what a subclass should contain. These abstract members only declare that a member of a particular type is required; it does not implement the member. Implementation of abstract members takes place within the derived class.
In Vb.net we use MustInherit in place of abstract in C#.
Example
[Vb.Net ]
Public MustInherit Class AbstractClass Sub New() End Sub Public MustOverride Sub Hello() Public MustOverride Function GetDouble(ByVal number As Integer) As Long Public MustOverride Function getHalf(ByVal number As Integer) As Long End Class Public Class drivedClass Inherits AbstractClass Public Overrides Sub Hello() ' Hello Message MessageBox.Show("Hello") End Sub Public Overrides Function GetDouble(ByVal number As Integer) As Long ' Get Double of any Number GetDouble = 2 * number End Function Public Overrides Function getHalf(ByVal number As Integer) As Long ' Get Half of any number getHalf = number / 2 End Function End Class
[C#]
public abstract class AbstractClass { public AbstractClass() { } public abstract void Hello(); public abstract long GetDouble(int number); public abstract long getHalf(int number); } public class drivedClass : AbstractClass { public override void Hello() { // Hello Message MessageBox.Show("Hello"); } public override long GetDouble(int number) { // Get Double of any Number return 2 * number; } public override long getHalf(int number) { // Get Half of any number return number / 2; } }