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).
Example
// 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);
}
}
Output
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'.
C# Language Specification
For more information, see the following sections in the C# Language Specification:
-
10.1.1.2 Sealed classes
-
10.5.5 Sealed methods
See Also