Lesson 17: Interfaces And Namespaces


1.Interfaces

An interface is defined as a syntactical contract that all the classes inheriting the interface should follow. The interface defines the 'what' part of the syntactical contract and the deriving classes define the 'how' part of the syntactical contract.

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. It often helps in providing a standard structure that the deriving classes would follow.

Abstract classes to some extent serve the same purpose, however, they are mostly used when only few methods are to be declared by the base class and the deriving class implements the functionalities.

Declaring Interfaces

Interfaces are declared using the interface keyword. It is similar to class declaration. Interface statements are public by default. Following is an example of an interface declaration:

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

Example

The following example demonstrates implementation of the above interface:

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();
      }
   }
}

When the above code is compiled and executed, it produces the following result:

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

 

2.Namespaces

A namespace is designed for providing a way to keep one set of names separate from another. The class names declared in one namespace does not conflict with the same class names declared in another.

Defining a Namespace

A namespace definition begins with the keyword namespace followed by the namespace name as follows:

namespace namespace_name
{
   // code declarations
}

To call the namespace-enabled version of either function or variable, prepend the namespace name as follows:

namespace_name.item_name;

The following program demonstrates use of namespaces:

using System;
namespace first_space
{
   class namespace_cl
   {
      public void func()
      {
         Console.WriteLine("Inside first_space");
      }
   }
}

namespace second_space
{
   class namespace_cl
   {
      public void func()
      {
         Console.WriteLine("Inside second_space");
      }
   }
}

class TestClass
{
   static void Main(string[] args)
   {
      first_space.namespace_cl fc = new first_space.namespace_cl();
      second_space.namespace_cl sc = new second_space.namespace_cl();
      fc.func();
      sc.func();
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following result:

Inside first_space
Inside second_space

The using Keyword

The using keyword states that the program is using the names in the given namespace. For example, we are using the System namespace in our programs. The class Console is defined there. We just write:

Console.WriteLine ("Hello there");

We could have written the fully qualified name as:

System.Console.WriteLine("Hello there");

You can also avoid prepending of namespaces with the using namespace directive. This directive tells the compiler that the subsequent code is making use of names in the specified namespace. The namespace is thus implied for the following code:

Let us rewrite our preceding example, with using directive:

using System;
using first_space;
using second_space;

namespace first_space
{
   class abc
   {
      public void func()
      {
         Console.WriteLine("Inside first_space");
      }
   }
}

namespace second_space
{
   class efg
   {
      public void func()
      {
         Console.WriteLine("Inside second_space");
      }
   }
}   

class TestClass
{
   static void Main(string[] args)
   {
      abc fc = new abc();
      efg sc = new efg();
      fc.func();
      sc.func();
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following result:

Inside first_space
Inside second_space

Nested Namespaces

You can define one namespace inside another namespace as follows:

namespace namespace_name1
{
   // code declarations
   namespace namespace_name2
   {
      // code declarations
   }
}

You can access members of nested namespace by using the dot (.) operator as follows:

using System;
using first_space;
using first_space.second_space;

namespace first_space
{
   class abc
   {
      public void func()
      {
         Console.WriteLine("Inside first_space");
      }
   }
   namespace second_space
   {
      class efg
      {
         public void func()
         {
            Console.WriteLine("Inside second_space");
         }
      }
   }   
}
 
class TestClass
{
   static void Main(string[] args)
   {
      abc fc = new abc();
      efg sc = new efg();
      fc.func();
      sc.func();
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following result:

Inside first_space
Inside second_space

 


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