csharp_namespaces.md - brainchildservices/curriculum GitHub Wiki

SLIDE-1

C# NAMESPACE

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.

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

                   namespace namespace_name {
                      // code declarations
                   }

SLIDE-1(DOWNWARD)

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();
                      }
                   }

                   after code is compiled and executed, output:

                               Inside first_space
                               Inside second_space

SLIDE-2

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");

This could have been written 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.

SLIDE-2(DOWNWARD)

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();
                      }
                   }

                   Output is same:
                   Inside first_space
                   Inside second_space

SLIDE-3

NESTED NAMESPACE

You can define one namespace inside another namespace as follows:

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

SLIDE-3(DOWNWARDS)

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();
                      }
                   }

                   Output:
                   Inside first_space
                   Inside second_space

Ref Link: https://www.tutorialspoint.com/csharp/csharp_namespaces.htm