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Namespaces in C#
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Namespaces are used to organize your code and to create globally unique types there by avoiding name collisions.
Namespaces are especially useful in large projects to avoid name collisions.
Let us look at an example how namespaces can be used for organizing code and avoiding name collisions.
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Let us take a Bank example. In this Bank we have 2 types of Customers
- PersonalCustomer
- EnterpriseCustomer
We have 2 Teams, Team A and Team B developing the Bank application.
- Team A develop all the classes required for Personal Customers.
- Team B develop all the classes required for Enterprise Customers.
These classes will finally be used in the main application. As Team A and Team B working are independently of each other it is very likely
that both the Teams can have a class Customer to represent their type of customer. This could lead to name
conflict(also called as name collisions). We cannot have two class(Types) with the same name in a single application.
To solve this problem we can use namespaces as shown in the below example.
- Team A which develops all the classes required for Personal Customers are with in PersonalCustomer namespace.
- Team B which develops all the classes required for Enterprise Customers are with in EnterpriseCustomer namespace.
In our example both the Teams are using the same name Customer to represent their respective customer.
Still we donot have a name collision because the classes are contained with in different namespaces.
The fully qualified names prevent the name collisions.
- Team A Customer fully qualified name : PersonalCustomer.Customer
- Team B Customer fully qualified name : EnterpriseCustomer.Customer
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using
System;
class
NameSpacesDemo
{
public
static void Main()
{
PersonalCustomer.Customer C1 = new
PersonalCustomer.Customer("Prasad");
EnterpriseCustomer.Customer C2 = new
EnterpriseCustomer.Customer("Giri");
}
}
namespace
PersonalCustomer
{
class
Customer
{
public Customer(string Name)
{
Console.WriteLine("Hello
Personal Customer, Welcome " + Name);
}
}
}
namespace
EnterpriseCustomer
{
class
Customer
{
public Customer(string Name)
{
Console.WriteLine("Hello
Enterprise Customer, Welcome " + Name);
}
}
}
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Microsoft has made extensive use of namespaces to organise .NET frameweork classes.
In our example in the first line we have using System directive. All the basic classes
and types are present in this namespace System. For example the Console class we
have used in our Main method is present in the System namespace. The fully qualified
name of the Console class is System.Console.
We can also use the using directive for the namespaces we have created. For example
to create an instance of our PersonalCustomer.Customer class we used.
- PersonalCustomer.Customer C1 = new PersonalCustomer.Customer("Prasad");
Instead we can use the using directive as shown in the below code snippet.
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using
System;
using
PersonalCustomer; // Using directive for our namespace
class
NameSpacesDemo
{
public
static void Main()
{
//We need not use the fully qualified name to create the instance
//as we are using the using PersonalCustomer; directive at the top.
Customer C1 = new
Customer("Prasad");
}
}
namespace
PersonalCustomer
{
class
Customer
{
public Customer(string Name)
{
Console.WriteLine("Hello
Personal Customer, Welcome " + Name);
}
}
} |
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Using an alias directive
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Aliases offer great readability. For example, I have 10 using directives at the
top of the program as shown in the below code snippet. In the Main method I am creating
an instance of the DataSet class. Now the confusion is, to which namespace does
the DataSet class belong? To avoid this type of confusion we can use aliases.
using
System;
using
System.CodeDom;
using
System.Data;
using
System.Globalization;
using
System.IO;
using
System.Net;
using
System.Reflection;
using
PersonalCustomer;
using
EnterpriseCustomer;
class
NameSpacesDemo
{
public
static void Main()
{
//To which namespace above does the Datset
//class belong to?
DataSet DS = new
DataSet();
}
}
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Below code snippet shows how to declare and use alias directive. In this code snippet
PC is an alias for PersonalCustomer namespace and EC for EnterpriseCustomer namespace.
To create an istance of PersonalCustomer.Customer class, I have prefixed the class
name with its respective alias.
using
System;
using
System.CodeDom;
using
System.Data;
using
System.Globalization;
using
System.IO;
using
System.Net;
using
System.Reflection;
using
PC = PersonalCustomer;
//PC alias for PersonalCustomer namespace
using
EC = EnterpriseCustomer;//EC alias for EnterpriseCustomer
namespace
class
NameSpacesDemo
{
public
static void Main()
{
PC.Customer
C1 = new PC.Customer("Prasad");
EC.Customer
C2 = new EC.Customer("Giri");
}
}
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Nesting namespaces
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Having a namespace inside another namespace is called nesting namespaces. You can nest namespaces to any level you want.
There are two ways to nest namespaces as shown below.
- We have nested namespaces to 3 levels.The fully qualified name of Customer class in the below code snippet is A.B.C.Customer
using
System;
namespace
A
{
namespace
B
{
namespace C
{
//Our Types(Classes,Interfaces,Structures,Delegates,Enumerations
etc..)
class Customer
{
//Class code
}
}
}
}
- Another approach to nest namespaces using the dot operator.
using
System;
namespace
A.B.C //Nesting namespaces using dot operator
{
//Our Types(Classes,Interfaces,Structures,Delegates,Enumerations
etc..)
class
Customer
{
//Class code
}
}
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Take awaya key points
- Even if you do not explicitly declare a namespace, a default namespace is created.
This unnamed namespace, sometimes called the global namespace, is present in every
file. Any identifier in the global namespace is available for use in a named namespace
- Namespaces have public access modifier by default. Explicit cccess modifiers and
attributes are not allowed on namespace declarations. It is a compile time error
to use explicit access modifiers or attributes on namespace declarations. We will
talk about access modifiers and attributes in our later article.
- Namespaces are used to organise your classes.
- Namespaces allow you to create globally unique names to your classes.
- Namespaces are especially useful in large projects to avoid name collisions.
- Namespaces are containers of Types(Classes,Structures,Interfaces,Enumerations,Delegates)
- Aliases can be used with namespaces to offer readability.
- Namespaces can be nested to any levels deep.
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Njoy Programming
ByPrasad Cherukuri
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