Csharp/CSharp Tutorial/Class/sealed

internal sealed class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

    public abstract class MyBase
    {
    }
    internal class MyClass : MyBase
    {
    }
    public interface IMyBaseInterface
    {
    }
    internal interface IMyBaseInterface2
    {
    }
    internal interface IMyInterface : IMyBaseInterface, IMyBaseInterface2
    {
    }
    internal sealed class MyComplexClass : MyClass, IMyInterface
    {
    }
    class Program
    {
        static void Main(string[] args)
        {
            MyComplexClass myObj = new MyComplexClass();
            Console.WriteLine(myObj.ToString());
        }
    }

Sealed Classes

sealed class MyClass
{
    MyClass() {}
}

Sealed methods

using System;
public class BaseClass
{
  public string lastName;
  public string firstName;
  public BaseClass(string lastName, string firstName)
  {
    this.lastName = lastName;
    this.firstName = firstName;
  }
  public virtual void Accelerate()
  {
    Console.WriteLine("In BaseClass Accelerate() method");
    Console.WriteLine(firstName + " accelerating");
  }
}
public class DerivedClass : BaseClass
{
  public DerivedClass(string lastName, string firstName) : base(lastName, firstName)
  {
  }
  sealed public override void Accelerate()
  {
    Console.WriteLine("In DerivedClass Accelerate() method");
    Console.WriteLine(firstName + " accelerating");
  }
}
class MainClass
{
  public static void Main()
  {
    DerivedClass myDerivedClass = new DerivedClass("A", "M");
    Console.WriteLine("Calling myDerivedClass.Accelerate()");
    myDerivedClass.Accelerate();
  }
}

Calling myDerivedClass.Accelerate()
In DerivedClass Accelerate() method
M accelerating

sealed types and methods.

To prevent a class from being inherited, precede its declaration with sealed.

sealed class FooSealed {}
class BaseClass
{
    protected virtual void Bar() { /*...*/ }
}
class Derived : BaseClass
{
    protected override sealed void Bar() { /* ... */ }
}