Interface concept in Programming

Interface Concept in Programming

Concept

Consider the you are the employee of IT company

Company provide you one standard card 

Property of card

1. Shape

2. Placement of words

3. Photo 

4. Info

Above properties are arranged as below format

Just imagine - If employee use different id card shapes and size. it will mess 

to over come this issue and implement standard for all employee we should create interface and implement when we create any employee id card

Key Points 

This is common interface for each and every employee of the company

Can we restrict to use of ID card interface?

No, it will be public by default.

Can we set any name or info directly into the ID card?

No, it will not allow to set into directly, it will just provide frame or structure

you can implement using it. if you try to implement any info, it violate interface property(when interface change all card will get impacted). 

Execution 

We have created the ICard interface
Now we can make any employee card.

interface ICard

{

        string CompanyName { get; set; }

        string FirstName { get; set; }

        string LastName { get; set; }

        string EmployeeID { get; set; }

        string DisplayEmployeeName();

}

//Create ID card for Parmanet employee

class ParmanentEmployeeCard : ICard

{

        public string CompanyName { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string EmployeeID { get; set; }

        public string DisplayEmployeeName()

        {  

            return $"{FirstName} {LastName}";

        }

}

class Program

{

        static void Main(string[] args)

        {

            ICard card = new ParmanentEmployeeCard();

            card.CompanyName = "XYZ Technology";

            card.EmployeeID = "2R451E1542";

            card.FirstName = "Sam";

            card.LastName = "adam";

            Console.WriteLine("Parmanent Employee");

            Console.WriteLine(card.CompanyName);

            Console.WriteLine(card.EmployeeID);                            Console.WriteLine(
                          card.DisplayEmployeeName());

            Console.ReadLine();

        }

    }

Output

Permanent Employee

XYZ Technology

2R451E1542

Sam adam

How we can handle other employee ICard like contract?

This interface will handle it like below

interface ICard

{

        string CompanyName { get; set; }

        string FirstName { get; set; }

        string LastName { get; set; }

        string EmployeeID { get; set; }

        string DisplayEmployeeName();

}

//Create ID card for Parmanet employee

class ParmanentEmployeeCard : ICard
{

        public string CompanyName { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string EmployeeID { get; set; }

        public string DisplayEmployeeName()

        {  

            return $"{FirstName} {LastName}";

        }

} 

//Create ID card for Parmanet employee

class ContractEmployee : ICard

{  

        public string CompanyName { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string EmployeeID { get; set; }

        public string DisplayEmployeeName()

        {

            return $"{FirstName} {LastName}";

        }

}

class Program
{

        static void Main(string[] args)

        {

            ICard card = new ParmanentEmployeeCard();

            card.CompanyName = "XYZ Technology";

            card.EmployeeID = "2R451E1542";

            card.FirstName = "Sam";

            card.LastName = "adam";

            Console.WriteLine("Parmanent Employee");

            Console.WriteLine(card.CompanyName);

            Console.WriteLine(card.EmployeeID);

            Console.WriteLine(
            card.DisplayEmployeeName());

            card = new ContractEmployee();

            card.CompanyName = "XYS Company";

            card.EmployeeID = "2245111654542";

            card.FirstName = "Jonh";

            card.LastName = "Mark";

            Console.WriteLine("\nContract Employee");

            Console.WriteLine(card.CompanyName);

            Console.WriteLine(card.EmployeeID);

            Console.WriteLine(
            card.DisplayEmployeeName()+"\n");

            
            Console.ReadLine();

        }

}

Output

Permanent Employee

XYZ Technology

2R451E1542

Sam adam

Contract Employee

XYS Company

2245111654542

Jonh Mark

Multiple Interfaces

    interface ICard
    {  

        string CompanyName { get; set; }

        string FirstName { get; set; }

        string LastName { get; set; }

        string EmployeeID { get; set; }       

        string DisplayEmployeeName();

    }

    interface ICardTemp

    {

        string VisitorName { get; set; }

        string ContactPerson { get; set; }

    }

//Create ID card for Permanent employee

 class PermanentEmployeeCard : ICard
  {

        public string DisplayEmployeeName()

        {

            return $"{FirstName} {LastName}";

        }

        public string CompanyName { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string EmployeeID { get; set; }

}

class ContractEmployee : ICard, ICardTemp
{

        public string CompanyName { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string EmployeeID { get; set; }

        public string VisitorName { get; set; }

        public string ContactPerson { get; set; }

        public void CreateTempCard()

        {

            Console.WriteLine($"Temp Card \n {VisitorName} \n {ContactPerson}");

        }

        public string DisplayEmployeeName()

        {

            return $"{FirstName} {LastName}";

        }
}

class Program

{

        static void Main(string[] args)

        {

            ICard card = new ParmanentEmployeeCard();

            card.CompanyName = "XYZ Technology";

            card.EmployeeID = "224511542";

            card.FirstName = "Sam";

            card.LastName = "adam";

            Console.WriteLine("Permanent Employee");

            Console.WriteLine(card.CompanyName);

            Console.WriteLine(card.EmployeeID);

            Console.WriteLine(card.DisplayEmployeeName());

            card = new ContractEmployee();

            card.CompanyName = "XYS Company";

            card.EmployeeID = "2245111654542";

            card.FirstName = "Jonh";

            card.LastName = "Mark";

            Console.WriteLine("\nContract Employee");

            Console.WriteLine(card.CompanyName);

            Console.WriteLine(card.EmployeeID);

            Console.WriteLine(card.DisplayEmployeeName()+"\n");

            ContractEmployee Tempcard = new ContractEmployee();

            Tempcard.VisitorName = "Robert";

            Tempcard.ContactPerson = "John Mark";

            Tempcard.CreateTempCard();

            Console.ReadLine();

        }
}

Output

Permanent Employee

XYZ Technology

224511542

Sam adam

Contract Employee

XYS Company

2245111654542

Jonh Mark

Temp Card

 Robert

 John Mark

Errors In Interface

1.Cannot contain fields

interface ICard

{

        string companyName;

}

Output

Error        CS0525        Interfaces cannot contain fields

2. Interface members cannot have a definition

interface ICard
{

        string CompanyName { get; set; }

        string FirstName { get; set; }

        string LastName { get; set; }

        string EmployeeID { get; set; }

        void DisplayName()

        {

            Console.WriteLine($"{FirstName} {LastName}");

        }

        string DisplayEmployeeName();

}

Output

Error        CS0531        'ICard.DisplayName()': interface members cannot have a definition

3.does not implement interface member

interface ICard
{

        string CompanyName { get; set; }

        string FirstName { get; set; }

        string LastName { get; set; }

        string EmployeeID { get; set; }

        string DisplayEmployeeName();

 }

//Create ID card for Parmanet employee

class ParmanentEmployeeCard : ICard

{

        public string CompanyName { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string EmployeeID { get; set; }

       //If you miss any of the method from interface, compile error

       //public string DisplayEmployeeName()

       // {  

       // return $"{FirstName} {LastName}";

        //}
}

Output

Error        CS0535        'ParmanentEmployeeCard' does not implement interface member 'ICard.DisplayEmployeeName()'

**** Sequence doesn't matter for implementation

4.cannot implement an interface member because it is not public

interface ICard

{

        string CompanyName { get; set; }

        string FirstName { get; set; }

        string LastName { get; set; }

        string EmployeeID { get; set; }

        string DisplayEmployeeName();

}

class ParmanentEmployeeCard : ICard

{

      string DisplayEmployeeName()

        {

            return $"{FirstName} {LastName}";

        }

        public string CompanyName { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string EmployeeID { get; set; }

}

Output

Error        CS0737        'ParmanentEmployeeCard' does not implement interface member 'ICard.DisplayEmployeeName()'.
'ParmanentEmployeeCard.DisplayEmployeeName()' cannot   
implement an interface member because it is not public.