Namespaces allow you to organize your code hierarchically and prevent naming collisions. Code is organized with more general namespace names at the top of the hierarchy and more specific names below. Namespaces group related classes and can be nested. To use classes from another namespace, the namespace name is prepended with dot notation. Namespaces are commonly used in C# to organize application code into logical groups.

1. C# Tutorial
Part 3 :
Namespaces
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2. • Namespaces allow you to create a system to
organize your code.
• A good way to organize your namespaces is via a
hierarchical system.
• You put the more general names at the top of the
hierarchy and get more specific as you go down.
• This hierarchical system can be represented by
nested namespaces. By placing code in different
sub-namespaces, you can keep your code organized.

3. • 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;

4. • Namespaces in C# are used to organize too many classes so that it can be easy to
handle the application.
• In a simple C# program, we use System.Console where System is the namespace and
Console is the class.
• To access the class of a namespace, we need to use namespacename.classname. We can
use using keyword so that we don't have to use complete name all the time.
• In C#, global namespace is the root namespace. The global::System will always refer
to the namespace "System" of .Net Framework.
• C# namespace example
• Let's see a simple example of namespace which contains one class "Program".
• using System;
• namespace ConsoleApplication1
• { class Program
• { static void Main(string[] args)
• { Console.WriteLine("Hello Namespace!");
• } } }
• Output:
• Hello Namespace!

5. • C# namespace example: by fully qualified name
• Let's see another example of namespace in C# where one namespace program
accesses another namespace program.
• using System;
• namespace First
• { public class Hello
• { public void sayHello() { Console.WriteLine("Hello First Namespace");
• }} }
• namespace Second
• { public class Hello
• { public void sayHello() { Console.WriteLine("Hello Second Namespace");
• } } }
• public class TestNamespace
• { public static void Main()
• { First.Hello h1 = new First.Hello();
• Second.Hello h2 = new Second.Hello();
• h1.sayHello();
• h2.sayHello();
• } }
• Output:
• Hello First Namespace Hello Second Namespace

6. • C# namespace example: by using keyword
• Let's see another example of namespace where we are using "using" keyword so that we don't have to
use complete name for accessing a namespace program.
• using System;
• using First;
• using Second;
• namespace First {
• public class Hello
• { public void sayHello()
• { Console.WriteLine("Hello Namespace");
• } } }
• namespace Second
• { public class Welcome
• { public void sayWelcome()
• { Console.WriteLine("Welcome Namespace");
• } } }
• public class TestNamespace
• { public static void Main()
• { Hello h1 = new Hello();
• Welcome w1 = new Welcome();
• h1.sayHello();
• w1.sayWelcome();
• } }
• Output:
• Hello Namespace Welcome Namespace

7. • namespace arun.CSharp.Namespaces
{
public class Hello
{
public string GetMessage()
{
return "Hello, world";
}}}
• Namespaces are hierarchical, and the name arun.CSharp.Namespaces is actually
shorthand for defining a namespace named arun that contains a namespace named
CSharp that itself contains a namespace named Namespaces, as in:
• namespace arun
{
namespace CSharp
{
namespace Namespaces
{....}
}}

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