Learn C#

1. Lesson 8
Learn C#. Series of C# lessons
http://csharp.honcharuk.me/lesson-8

2. Agenda
• Sealed
• Abstract classes
• Interfaces
• Abstract Class versus Interface

3. Sealed
• Sealed modifier prevents other classes from inheriting from it
sealed class A
{
}
//Gives an error, due to sealed class A
class B : A
{
}

4. Abstract classes
• Abstract class cannot be instantiated, and is frequently either partially
implemented, or not at all implemented
public abstract class Country
{
public string Name { get; set; }
public string Currency { get; set; }
public void PrintInformation()
{
Console.WriteLine(Name);
Console.WriteLine(Currency);
Console.WriteLine(this.GetFlagDescription());
}
public abstract string GetFlagDescription();
}

5. Interfaces
• An interface is not a class.
• An interface is defined as a syntactical contract that all the classes
inheriting the interface should follow.
public interface IAlcohol
{
double AlcoholByVolume { get; set; }
double GetMaximumAllowedWightForHuman();
}

6. Abstract Class versus Interface
Feature Interface Abstract class
Multiple inheritance YES NO
Default implementation NO YES
Access Modfiers
NO (Everything goes
public by default)
YES
Fields and Constants NO YES

7. Thank you!
Questions?