C# : Sealed class , Interface : Part 10

Sealed class

• Once the class is marked as sealed than it cannot be used as inheritance, or as a base class.

Interface

• It is used only for declaration, implementation is not done here.
• All the declaration are public by default.
• It contains only declarations no fields.
• If a class inherits from an interface than it must provide implementation for all interface members, other wise it will provide compile time error.
• Class cannot inherit from more than one class where as it can inherit from more than one interface.

e.g. 

namespace Interface

{

    public interface Interface1

    {

        int Add(int a, int b);

    }

    public class Class1 : Interface1

    {

         

        public int Add(int a, int b)

        {

            return a + b;

        }

    }

    class Program

    {

        static void Main(string[] args)

        {

            Class1 objClass1 = new Class1();

            var result = objClass1.Add(3, 6);

        }

    }

}

Explicit Implementation of Interface

• If the class inherits from two or more interface and all of them have same method with same signature, than there comes the need of explicit implementation.
• If Explicit implementation is not done, it will not give any compile time error, but method from which interface is invoked is not cleared.
• Thus explicit implementation of interface is done by type casting of object.

e.g. 1 type casting is not done

namespace ExplicitInterfceImplementation

{

    public interface Interface1

    {

        int Add(int a, int b);

    }

    public interface Interface2

    {

        int Add(int a, int b);

    }

    public class Class1 : Interface1, Interface2

    {

        public int Add(int a, int b)

        {

            return a + b;

        }

    }

    class Program

    {

        static void Main(string[] args)

        {

            Class1 objClass1 = new Class1();

            var result = objClass1.Add(3, 6);

        }

    }

}

e.g. 2 With type casting implementation of interface

namespace ExplicitInterfceImplementation

{

    public interface Interface1

    {

        int Add(int a, int b);

    }

    public interface Interface2

    {

        int Add(int a, int b);

    }

    public class Class1 : Interface1, Interface2

    {

        public int Add(int a, int b)

        {

            return a + b;

        }

    }

    class Program

    {

        static void Main(string[] args)

        {

            Class1 objClass1 = new Class1();

            var result = ((Interface1)objClass1).Add(3, 6);

        }

    }

}