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Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here.

sealed (C# Reference)

The sealed modifier can be applied to classes, instance methods and properties. A sealed class cannot be inherited. A sealed method overrides a method in a base class, but itself cannot be overridden further in any derived class. When applied to a method or property, the sealed modifier must always be used with override (C# Reference).

Use the sealed modifier in a class declaration to prevent inheritance of the class, as in this example:


      sealed class SealedClass 
{
    public int x; 
    public int y;
}

It is an error to use a sealed class as a base class or to use the abstract modifier with a sealed class.

Structs are implicitly sealed; therefore, they cannot be inherited.

For more information about inheritance, see Inheritance (C# Programming Guide).

// cs_sealed_keyword.cs
using System;
sealed class SealedClass
{
    public int x;
    public int y;
}

class MainClass
{
    static void Main()
    {
        SealedClass sc = new SealedClass();
        sc.x = 110;
        sc.y = 150;
        Console.WriteLine("x = {0}, y = {1}", sc.x, sc.y);
    }
}

 
x = 110, y = 150

In the preceding example, if you attempt to inherit from the sealed class by using a statement like this:

class MyDerivedC: SealedClass {} // Error

you will get the error message:

'MyDerivedC' cannot inherit from sealed class 'SealedClass'.

For more information, see the following sections in the C# Language Specification:

  • 10.1.1.2 Sealed classes

  • 10.5.5 Sealed methods

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