In the following example, Z inherits from Y but Z cannot override the virtual function F that is declared in X and sealed in Y.
class X
{
protected virtual void F() { Console.WriteLine("X.F"); }
protected virtual void F2() { Console.WriteLine("X.F2"); }
}
class Y : X
{
sealed protected override void F() { Console.WriteLine("Y.F"); }
protected override void F2() { Console.WriteLine("X.F3"); }
}
class Z : Y
{
// Attempting to override F causes compiler error CS0239.
// protected override void F() { Console.WriteLine("C.F"); }
// Overriding F2 is allowed.
protected override void F2() { Console.WriteLine("Z.F2"); }
}
When you define new methods or properties in a class, you can prevent deriving classes from overriding them by not declaring them as virtual.
It is an error to use the abstract modifier with a sealed class, because an abstract class must be inherited by a class that provides an implementation of the abstract methods or properties.
When applied to a method or property, the sealed modifier must always be used with override.
Because structs are implicitly sealed, they cannot be inherited.
For more information, see Inheritance (C# Programming Guide).
sealed class SealedClass
{
public int x;
public int y;
}
class SealedTest2
{
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 previous example, you might try to inherit from the sealed class by using the following statement:
class MyDerivedC: SealedClass {} // Error
The result is an error message:
'MyDerivedC' cannot inherit from sealed class 'SealedClass'.