C# Sealed

C# sealed keyword applies restrictions on the class and method. If you create a sealed class, it cannot be derived. If you create a sealed method, it cannot be overridden.

Note

Structs are implicitly sealed therefore they can't be inherited.

C# Sealed class

C# sealed class cannot be derived by any class. Let's see an example of sealed class in C#.

Example

snippet

using System;
sealed public class Animal{
    public void eat() { Console.WriteLine("eating..."); }
}
public class Dog: Animal
{
    public void bark() { Console.WriteLine("barking..."); }
}
public class TestSealed
{
    public static void Main()
    {
        Dog d = new Dog();
        d.eat();
        d.bark();


    }
}

Output

Compile Time Error: 'Dog': cannot derive from sealed type 'Animal'

C# Sealed method

The sealed method in C# cannot be overridden further. It must be used with override keyword in method.

Example #1

Let's see an example of sealed method in C#.

snippet

using System;
public class Animal{
    public virtual void eat() { Console.WriteLine("eating..."); }
    public virtual void run() { Console.WriteLine("running..."); }

}
public class Dog: Animal
{
    public override void eat() { Console.WriteLine("eating bread..."); }
    public sealed override void run() { 
	Console.WriteLine("running very fast..."); 
    }
}
public class BabyDog : Dog
{
    public override void eat() { Console.WriteLine("eating biscuits..."); }
    public override void run() { Console.WriteLine("running slowly..."); }
}
public class TestSealed
{
    public static void Main()
    {
        BabyDog d = new BabyDog();
        d.eat();
        d.run();
    }
}

Output

Compile Time Error: 'BabyDog.run()': cannot override inherited member 'Dog.run()' because it is sealed

Note

Local variables can't be sealed.

Example #2

snippet

using System;
public class TestSealed
{
    public static void Main()
    {
        sealed int x = 10;
        x++;
        Console.WriteLine(x);
    }
}

Output

Compile Time Error: Invalid expression term 'sealed'