How to declare and use Interfaces in C#?

Interfaces define properties, methods, and events, which are the members of the interface. Interfaces contain only the declaration of the members. It is the responsibility of the deriving class to define the members.

Let us declare interfaces −

public interface ITransactions {    // interface members    void showTransaction();    double getAmount(); }

The following is an example showing how to declare and use Interfaces in C# −

Example

 Live Demo

using System.Collections.Generic; using System.Linq; using System.Text; using System; namespace InterfaceApplication {    public interface ITransactions {       // interface members       void showTransaction();       double getAmount();    }    public class Transaction : ITransactions {       private string tCode;       private string date;       private double amount;       public Transaction() {          tCode = " ";          date = " ";          amount = 0.0;       }       public Transaction(string c, string d, double a) {          tCode = c;          date = d;          amount = a;       }       public double getAmount() {          return amount;       }       public void showTransaction() {          Console.WriteLine("Transaction: {0}", tCode);          Console.WriteLine("Date: {0}", date);          Console.WriteLine("Amount: {0}", getAmount());       }    }    class Tester {       static void Main(string[] args) {          Transaction t1 = new Transaction("001", "8/10/2012", 78900.00);          Transaction t2 = new Transaction("002", "9/10/2012", 451900.00);          t1.showTransaction();          t2.showTransaction();          Console.ReadKey();       }    } }

Output

Transaction: 001 Date: 8/10/2012 Amount: 78900 Transaction: 002 Date: 9/10/2012 Amount: 451900